Chapter X — 119 — Drosera 



It was observed by Schmid that during the absorption of materials 

 from the bodies of prey, the starch content of the tissues at the base 

 of the tentacles is lost. According to Spoehr (1923) the amino acids 

 are concerned with the metabolism of starch. From this Geessler 

 (1928) was prompted to investigate the influence of salts on the me- 

 tabolism of starch in the leaf of Drosera capensis. He found that in 

 this species, when the leaf is fed with insects or with various salts, 

 there is a disappearance of starch from the leaf. The leaves of D. 

 capensis are in summertime heavily loaded with starch. The starch 

 content is not lowered even when the plant is kept in the dark. Even 

 after 45 days in the dark in contact with distilled water, the leaf (at 

 temp. 36-38° C.) showed no reduction in starch. The sugar con- 

 tent is minute. In winter the leaves are starch-free, but there is as 

 little sugar as in summer. These facts, together with the high respira- 

 tory intensity, indicated to Giessler that the physiology of Drosera 

 resembles rather that of the animal than of the plant, in that there 

 is a protein respiration. He suggests that the starch is used in the 

 secretion of mucilage and in supplying the energy for the bending of 

 the tentacles and leaf blade in response to stimulation. In support of 

 his thesis he points out the abundant occurrence of labile albumin 

 (LoEw) in many carnivorous plants and mentions in support of this 

 the work of Erna Janson on aggregation, to which reference is made 

 elsewhere. It has often been asked if the carnivorous plants are not 

 animal-like in view of their habits, and this is at present answered as 

 above. 



The absence of a palisade tissue in Drosera, already mentioned, is 

 not confined to this genus, but is generally though not universally true 

 of carnivorous plants. This lack stands, according to Schmid, in re- 

 lation to insectivory, the latter affording compensation. But Kos- 

 TYTSCHEW questioned this, and did experiments which he regarded as 

 proving that both Drosera and Pinguicula are quite as active as the 

 control plants which he used. As his figures are the only ones avail- 

 able, I give them. The amount of CO2 assimilated per i dm^ of leaf 

 surface: Drosera rotimdifolia, 4 cc, Tussilago farfara (control) 3.8 cc, 

 Pinguicula vulgaris, 38.4 cc, Aegopodium podagraria 18. i cc. 



"Thus KosTYTSCHEw's experiments answered the question whether a carnivorous plant 

 can obtain its carbon nutrition through photosynthesis in the affirmative. The scant ex- 

 perimental data show, and the text implies, that Drosera and Pinguicula leaves, which 

 have not had access to animal nutrition for some time, carry on photosynthesis at a normal 

 rate. The observed rates are in good agreement with those estabhshed by Willstatter 

 and Stoll for a wide variety of green plants. Kostytschew's comparisons with Aiiricu- 

 laria and Lenina also bear this out. 



"From his data on photos>Tithesis of Drosera it appears, however, that the rate of 

 carbon dioxide assimilation would have increased materially after feeding the plants with 

 insects. The experimental details have not been recorded in sufficient detail to permit of 

 a definitive decision. But the discovery of a measurable effect of the ingestion of animal 

 material on the rate of photosynthesis would open up a new approach to a study of the 

 problem of photosynthesis itself. The importance of such a possibiUty made it an easy 

 matter to obtain the co-operation of Dr. W. Arnold in carrying out some preliminary ex- 

 periments. 



"Drosera and Pinguicula plants, previously not animal fed, were used for the experi- 

 ments. Single leaves were placed in distilled water in the center-cups of Warburg vessels. 

 A mixture of sodium carbonate and bicarbonate was introduced into the main chamber 

 in order to insure a constant carbon dioxide pressure in the gas phase. Photosynthesis 



