Chapter X — 127 — Drosera 



In support of the idea he recalls the case of the trap of Utricularia, 

 which is known to excrete water from the glands on its outer surface 

 (glands not much dissimilar from the ones in question) and to absorb 

 nutrition and water from the interior by means of the bifid and quad- 

 rifid trichome glands. Since these two sets of glands in Utricularia are 

 the only non-cuticularized areas of the inner and outer surfaces of the 

 trap and since the cuticle elsewhere is impermeable {e.g. to dyes) we 

 are forced to recognize its pecuHar glandular action as involving the 

 two sets of glands, as Czaja, Merl and Nold have beHeved. This 

 view would harmonize our ideas about the two apparently widely 

 different structures, leaf and trap. 



The free flow of watery secretion observed during the earlier stages 

 of digestion or just previous thereto, even if Konopk.a.'s view is correct, 

 does not preclude the possibility that the sessile glands may not con- 

 tribute to the efficiency of the leaf by exercising the function of ab- 

 sorption as well. We may, therefore, direct our attention briefly to 

 the specific question of locus or loci of absorption of the leaf. 



The locus of absorption. — Previous to the studies of Oudman, there 

 had always been a vagueness about the point of entrance of substances 

 absorbed by the leaf. Three possibilities there are: (i) that they enter 

 through the tentacles; or (2) through the papiUae; and (j) through the 

 epidermis, which according to Nitschke, has no cuticle. The last may 

 be at once excluded as Nitschke's statement is not true. Aside from 

 direct proof with sulfuric acid, the dift'usion of e.g. caffeine (Kok) into 

 the leaf takes place through the papillae, and not through nearby 

 epidermal cells. 



With regard to the tentacles the fact of aggregation in the stalk 

 cells following on the application of various substances (insects, caffeine, 

 etc.) would seem to indicate at once that absorption can and does take 

 place through the glands. Darwin indeed regarded aggregation as 

 proof of absorption. Pfeffer, however, pointed out that this might 

 be the result of the stimulating eft'ect of minimal quantities of ma- 

 terial with no quantitative relations indicating absorption. Some such 

 substance has been thought to be necessary to procure aggregation, 

 that is, a specific aggregation-stimulating substance formed in the 

 gland (Akerman, 191 7; Coelingh, 1929). Ali Kok determined the 

 rate of transport of caffeine from the glands into the tentacle stalks. 

 Changes in the structure of the cytoplasm and nucleus (studies by 

 HuiE, Rosenberg, Konopka and Ziegenspeck, and Kruck on Utricu- 

 laria), were referred by them to the activity of these structures (cyto- 

 plasm and nucleus) in response to the absorption of various foods. 

 Taking up of food by the tentacles has been generally assumed, as 

 e.g. by GoEBEL, Fenner, Ruschmann. Oudman points out, however, 

 that there is little positive information and that even if the tentacles 

 do absorb, their role may be small and of secondary significance. 



That the papillae, small sessile glands of various sizes, smallest on 

 the tentacle stalks, largest on the leaf blade, where they occur on both 

 surfaces, are concerned in absorption has been expressed by Darv;in, 

 and by Rosenberg, both of whom saw the ready passage of sub- 

 stances through them into the tissues. Rosenberg used methylene 

 blue (as I have repeatedly done). Fenner and Coelingh, as also 



