It is often said that Doctor Who is at its most successful when its roots are showing, which perhaps explains the success of 'The Seeds of Doom'. The most obvious influences on this story are The Thing, to which the first two episodes have notable similarities, and The Quatermass Experiment, in which an alien influence infects an astronaut and transforms him into a giant tentacled mass that threatens to germinate and eradicate all human life on the planet. In addition to these other influences, 'The Seeds of Doom' is heavily based on Phillip Levene's earlier Avengers script Man-Eater of Surrey Green, in which an alien seed pod lands on Earth and is nurtured by a wealthy botanist, over whom it exerts telepathic control. In addition to this, an eccentric female botanist, of whom Amelia Ducat is rather reminiscent, aids Steed and Mrs. Peel. With so many obvious influences, 'The Seeds of Doom' could have been something of a mixed bag, but with six episodes and two major locations it manages to combine its multiple ingredients with considerable success.
With the danger of padding always a problem with six part Doctor Who stories, 'The Seeds of Doom' successfully avoids this problem by essentially taking the structure of a two-part story followed by a four-part story, one of only two such six parters in the series history. Thus, the first two episodes concern the discovery of the two Krynoid pods in Antarctica, whilst the four remaining episodes focus on Harrison Chase's insane attempt to unleash a Krynoid on Earth. It is these first two episodes that are obviously influenced by The Thing, as scientists in the Antarctic uncover a buried alien lifeform, but in this case the lifeform is of course the first pod and it infects Winlett. The first two episodes are very atmospheric, managing to overcome budgetary limitations with a confident swagger; brooding incidental music accompanies the scientists' discovery of the pod and manages to make a throbbing cabbage look sinister, and the threat represented by the pod is emphasised further by the Doctor's doom-laden warnings about the nature of the Krynoid. The actual transformation of Winlett is realised using make-up that resembles green foam rubber, but as with the bubble-plastic Wirrn Larvae in 'The Ark in Space', it works because both script and actors take it so very seriously. The Doctor's suggestion of amputating Winlett's arm adds an additional detail of reality, as the occupants of the base struggle to deal with a wholly unexpected situation with minimal resources and no outside help. In theory, setting a story in Antarctica should be a very bad idea in budget and effects terms, and inevitably there is much use made of CSO, polystyrene snow, and stock footage, resulting in a recreation of Antarctica which looks cheaper and less effective than that used on 'The Tenth Planet'. Mercifully, exterior scenes are kept to a minimum, and once again the script and acting paper over these potentially dodgy scenes.
It has been suggested that Robert Banks Stewart's unfamiliarity with Doctor Who results in a story more reminiscent of The Avengers, with a great deal more gritty realism than usual. I agree with this to an extent, in that there are certainly similarities with The Avengers on display; the Doctor and Sarah are sent to Antarctica in Episode One in a helicopter and by a ministry to, in effect, act as troubleshooters. In addition, there is an unusual amount of gun usage, and Chase is very much in the mold of a diabolical mastermind straight out of The Avengers. On the other hand, The Avengers (or to be precise, the Emma Peel era) is also known for its wit and whimsy, with eccentricity as important as plot; 'The Seeds of Doom' boasts an eccentric villain and indeed another eccentric in the form of Amelia Ducat, and also has moments of wit, but I wouldn't say that it feels much like The Avengers. Whilst unlike Doctor Who, The Avengers was always aimed at an older audience, its more adult feel lies in directions other than violence, especially by the Emma Peel era, during which highly stylized and choreographed fights were the norm, not Molotov cocktails and machine guns. Instead, 'The Seeds of Doom' feels more like what it is; grittier than usual Doctor Who. Thus we have the Doctor resorting to physical violence with his fists, and also memorably pulling a gun on Chase. In return, Scorby throws him around in the compost room and he is visibly rattled as a result. It is also perhaps worth noting that whilst Steed (and of course, often the Doctor himself) usually faces danger without losing his composure, here the Doctor clearly suffers, as summed up neatly by Chase's final scene, as he tries to drag the Doctor into the crusher, even as the Doctor is trying to save Chase's life; the Doctor doesn't follow Chase's death with a quip, he just looks genuinely shaken.
Regardless of whether or not 'The Seeds of Doom' more closely resembles The Avengers than Doctor Who, it remains a highly effective story. Part of this success is down to the Krynoids. Massive, tentacled, intelligent, carnivorous plants from outer space are not common even in Doctor Who, and on paper the Krynoids look like a bad idea; animated plants are always at risk of looking silly, and tentacles are notoriously difficult to realize effectively. Nevertheless, the Krynoid - both of them - generally works very well. The use of a recycled, repainted Axon monster costume from 'The Claws of Axos' works well, as does the model work of the giant Krynoid squatting over Chase's Mansion in Episode Six; even the tentacle that bursts into the building in the final episode looks good. The eight-foot high Krynoid is rather less impressive, and during the Episode Four cliffhanger it is amusingly reminiscent of the Slyther. Another unfortunate decision is to let it speak, given that the chosen vocal effect makes it sound like the Wonderful Krynoid of Oz. These are however, minor shortcomings and in fact the execution is essential to the success of 'The Seeds of Doom', given that the concept can't help but sound vaguely silly; killer vegetation is not an idea that I personally find especially scary. Nevertheless, it works because of the approach taken. The Krynoid itself works because big tentacled aliens tend to make an impression, but far more impressive an achievement is the realisation of the hostile native plant life as the Krynoid begins to exert its influence over the plants of Chase's estate. Wisely director Douglas Camfield avoids the use of stop-motion animation or vines on wires, and resorts to the simple approach of waving plants about. This sounds daft, but it works surprisingly well thanks again to the acting and direction, not to mention the incidental score. Scorby's death is a good example; dragged under water by animated pondweeds, John Challis's acting convinces that Scorby is genuinely fighting for his life, the scene is starkly shot and the foreboding incidental music completes the effect, making it a powerful scene. The Krynoid also works because of what it does; a human being infected by and transformed into an alien monster is not an original idea in science fiction (or Doctor Who), but it seldom fails to work. Winlett's transformation is given added effect by the Doctor's grim warnings of what will ultimately happen to him and the fact that he suggests amputation simply because he's running out of ideas, but it is Keeler's transformation which is by far the most horrific. Here, the effect is heightened by Chase's inhuman attitude to Keeler's inhuman transform, as his zealous fascination with the Krynoid deafens him to Keeler's pitiful pleas for medical aid. Even more disturbing is the scene of Hargreaves bringing him a plate of raw meat; on seeing it, Keeler's look of helpless anger gives way to an expression of ravenous hunger.
Speaking of Scorby and Keeler, with the first Krynoid stranded in the middle of icy tundra with very little to eat and no plant life to control, the most immediate threat to the Doctor and Sarah is Chase's henchmen. Keeler is basically along as a botanist whom Chase owns "body and soul", and who objects to Scorby's brutal tactics but is too weak to actually stand up to him. His indecisive character works well as a contrast to Scorby and Mark Jones' tortured portrayal works particularly well when the second pod infects him. In many ways however, Scorby is by far the most interesting character. It is established early on that he is, as to use the Doctor's vernacular, a "stooge" for Chase, but unusually for Doctor Who he gets a very meaty role for a mere stooge. Despite acting under orders from a far more dangerous nutter, he remains a significant enough threat on his own to cause problems for the Doctor. The reason being of course that he is utterly ruthless and highly professional. Although the Doctor later overpowers him, Scorby gives as good as he gets as he throws the Doctor around in the compost room, and generally fares well against a being that has destroyed near-omnipotent demigods. His later alliance with the Doctor and Sarah to save his own skin works well, demonstrating his overwhelming drive to survive, something he addresses in Episode Five, as he tells Sarah that he has always relied entirely on himself, and nobody else, during a lengthy and probably bloody career. This utter selfishness immediately explains his character perfectly, a ruthless mercenary who will do anything for money, unless it threatens his own survival. Interestingly, and refreshingly, during the final two episodes, he shows absolutely no interest in revenge on the Doctor or Sarah for previous indignities aside from a couple of guarded threats, which seem more like a show of strength than anything else. Appropriately, Challis portrays Scorby as an efficient thug, and it is impressive that a character who is neither of the main villains can be so interesting without being acted with the charisma of psychopaths such as Reegan from 'The Ambassadors of Death'.
And then there's Harrison Chase. In a season featuring such villains as Broton, Sutekh and Morbius, it is easy to overlook Chase, who isn't even technically the main protagonist of the story. Yet with only the villainy of a giant vegetable to upstage, Tony Beckley steals the show. Chase is a superb villain; a complete lunatic played perfectly without being over the top. Initially, Chase seems almost comical, a neatly suited leather gloved and arguably slightly camp maniac millionaire whose obsession with plants is so great that it places him amongst Doctor Who's highest echelons of utter madmen. When he plays a symphony to the plants in the greenhouse it treads a fine line between ludicrous and sinister, but Beckley pulls it off perfectly. As the end of Episode Three approaches however, he becomes much scarier; Keeler's protestation that what he intends to do to Sarah is inhuman meeting with the chilling response "I don't care. I must see what happens when the Krynoid touches human flesh". As he "nurtures" the terrified Keeler he becomes even more disturbing and by the time he makes contact with the Krynoid in Episode Five he's already so overwhelmed by his fascination with the creature that it's hard to tell whether he's really possessed or not. A villain with a giant crushing machine just sounds silly, but Beckley's acting and Camfield's direction mean that when the Doctor is tied up in the crusher, its just tense, especially with Baker at the height of his powers and yelling at Sarah to turn it off. Chase's death, as he is dragged into the crusher and pumped into his gardens, is entirely appropriate; it's also chilling, as he determinedly attempts to take the Doctor with him, whilst the Doctor is trying desperately to save him.
The rest of the guest cast is, at worst, adequate; Kenneth Gilbert as Dunbar and Michael Barrington as Sir Colin are unmemorable but competent, but Sylvia Coleridge is hugely entertaining as the eccentric and rather endearing Amelia Ducat. I also feel the need to mention Seymour Green, but only because of his amusingly appropriate name. The direction, mentioned briefly above, is very good, particularly during the last four episodes once the CSO Antarctic is out of the way; the location filming is stunning, and meshes perfectly with the impressive interior sets of Chase's mansion.
Finally, I should just mention UNIT. This is the organization's last semi-regular appearance, and boasts none of the regulars, with Major Beresford standing in for the Brigadier and neither Mike Yates nor Sergeant Benton anywhere to be seen. It has been suggested that this is rather a downbeat farewell for UNIT, and indeed John Acheson's Major Beresford is forgettable, but it's also worth noting that after descending into cosy incompetence later on during the Pertwee era, UNIT does literally get to save the world here, as they are responsible for blowing the Krynoid to pieces. It isn't the most ingenious means of defeating the monster, but it works, and as UNIT's last act in Doctor Who for a very long time, it isn't a bad way to sign off.