Intro- —5— tiuction 



are captured, as, e.g. in the case of the catch-fly {Silene). Suspecting 

 that many such plants might turn out to be carnivorous Darwin 

 investigated the behavior of some of them: Saxifraga umbrosa, S. 

 rotundijolia (?), Primula sinensis, Pelargonium zonale, Erica tetralix, 

 Mirabilis longifolia and Nicotiana tabacum. But while he thought to 

 have proved that the hairs of these plants can in some instances absorb 

 organic nutrients, he regretted that he did not try if they could "digest 

 or render soluble animal substances." Fermi and Buscaglione in 1899 

 tried some of these and still others {Martynia, Hydrolea, Sparmannia) 

 for digestion with negative results, whereas those of the recognized 

 carnivorous plants which they tried were positive. This brings into 

 relief the fact that there are many plants which resemble our carniv- 

 orous plants so closely that we can decide about them only through 

 experiment. 



Though the glands involved are in structure similar in some cases 

 {Byhlis, Pinguicula) to those found among other plants, those of Dro- 

 sophyllum and Drosera, fundamentally the same in structure in both, 

 are unique as entireties. Those of Drosera are raised on emergencies 

 which display motility in no respect different, except perhaps in speed, 

 from that of ordinary growth. The histological elements of the glands 

 are common enough; again it is the constellation of characters which 



stands out. 



The most complete analog to a carnivorous plant of this type is one 

 which was until recently regarded as one itself. This is the Roridula, 

 of which there are two species, in South Africa. I myself included it 

 among the carnivores in an account pubhshed in 1933. Since that 

 time, on receiving material preserved in formalin from Munich, it was 

 at once apparent that the secretion which appears as glistening drop- 

 lets in the living plant, was intact and still adherent to the glands, and 

 could therefore not be a mucilage. Had the preservative been alcohol 

 this might have escaped attention. The leaves bear many tentacles 

 superficially similar to those of Drosera. Examination showed them to 

 be anatomically quite different, and that they exude a resinous secre- 

 tion. There are no other glands, so that on this evidence the carniv- 

 orous habit seems to be quite excluded (Lloyd, 1934)- These two 

 species, relatives of Drosera, are, like them and Byblis, used by certain 

 insects (certain bugs and crab spiders) as habitual feeding grounds. 

 When insects are freshly caught, they are attacked for their body juices. 

 How these commensal forms avoid capture is another matter, but an 

 interesting one. 



The trap of Dionaea and Aldrovanda, with its close resemblance to 

 a steel-trap, has been, and still is regarded by some as "perhaps the 

 most marvellous in the world," to quote Morren (1875) who, in say- 

 ing this, was only repeating what Darwin had already said. It appears 

 to be quite unique when regarded as a total mechanism. But an analog, 

 in some measure at any rate, was suggested by Delpino, quoted by 

 Hooker in his Presidential Address at the meeting of the British 

 Association for the Advancement of Science in 1874. Hooker had 

 already described a plant from Tierra del Fuego under the name Caliha 

 dioneaefolia "which," Delpino in effect remarked, "is so analogous in 

 the structure of its leaves to Dionaea, that it is difficult to resist the 



