Chapter X — 149 — Drosera 



found that some (albumin, pepsin, peptone, phosphoric acid, ethyl 

 alcohol) cause swelling of the protoplasm and the accompanying ap- 

 pearances of aggregation, while others (basic substances such as am- 

 monia, carbonates of ammonia, sodium or potassium, alkaloids), do not 

 cause protoplasmic swelling, but only a precipitation in the vacuole 

 with unchanged volume. Further, that these latter substances can in- 

 hibit the action of the former. 



The difference between true aggregation and " granulation" in 

 which merely precipitation occurs within the vacuole, is emphasized by 

 the results of plasmolytic studies. Akerman found that during ag- 

 gregation there is an increase in turgor pressure of about 5 atm. in the 

 cells involved. De Vries, it is true, found no changes while G.^rdener 

 beheved that they " lose their turgidity" (he made no experiments to 

 show this). As Coelingh points out, the difference in the use of the 

 terms turgidity and turgor pressure (dependent on the concentration of 

 the sap) is to be noted. In the case of cells in which precipitation oc- 

 curred, there is no change. 



From experiments to determine if there is an influence of the gland 

 on aggregation, Akerm.a.n found that in pieces of tentacle stalk from 

 which (a) the gland with one-third and (b) with two-thirds of the stalk 

 removed, no aggregation at all could be procured in the remaining 

 portion of the tentacle. If only the gland and one-third of the stalk 

 had been removed, a weak or no aggregation occurred, according to the 

 test substance used. Akerman tried eight agents. 



That injury is not involved is shown by the fact that aggregation 

 intervenes in small pieces of the upper region of the tentacle when pep- 

 sin or meat extract are applied. 



These results in Akerman's opinion pointed to the presence of a 

 substance, resident or formed in the gland and in the more apical stalk 

 cells, which can on suitable stimulation procure aggregation. It looks 

 therefore, as if two substances are required to cause aggregation, one 

 inherent and one which must be supplied from the outside as a stimu- 

 lant. As Darwin recorded, however, aggregation occurs when the 

 tentacles are stimulated by mechanical means only. If a second sub- 

 stance is required, this must mean that the second substance is also 

 formed in the gland when so stimulated {see beyond). 



Miss Coelingh, working at Utrecht, where the study of growth 

 substances was then being actively prosecuted, repeated some of Aker- 

 man's work, supporting his conclusion that during the progress of ag- 

 gregation there is an increase in the osmotic value of the sap, but that 

 this also takes place when the tentacles are successfully stimulated by 

 mechanical means. Having also verified Akerman's observation on the 

 effect of the gland on aggregation in the stalk (finding shght but 

 not significant differences) Coelingh proceeded to test the value of 

 his theory of an aggregation-promoting substance. To this end she 

 made extracts of glands in distilled water. Such extracts may be 

 preserved dry, and can then withstand heating to 100° C. In 

 order to determine the virtue of gland-extract, Coelingh proceeded 

 to obtain "empty" pieces of tentacle stalk, that is, such as would 

 not show aggregation when a "stimulating" agent (beef extract) was 

 apphed. Such were obtained of four kinds: (/) small strips of leaf 



