Chapter X —145— Drosera 



ing the glands into contact with the prey. The tropistic movement is 

 slower. The case of D. hinata well illustrates the behavior, because of 

 the cylindrical form of the leaf. A small fragment of meat was placed 

 on an outer surface tentacle. This responded at first quickly, and in 

 the course of five hours brought the prey into contact with the discal 

 tentacles. In two hours the nearby outer surface tentacles began their 

 excursions which were at first (for four and a half hours) nastic. The 

 next morning it was evident that tropistic movements had set in, 

 since by then all the glands were in contact with the prey. When, 

 however, in this species the stimulus is applied to the discal tentacles, 

 the reactions of the outer surface tentacles are entirely, or very nearly 

 entirely, tropistic. The case of D. capensis was of peculiar interest, 

 since in this species stimulus of an outer tentacle procured tropistic 

 reactions of its neighbors so that their glands would have travelled 

 the shortest way to the place where the prey was deposited on the 

 discal tentacles (the completion of the movement was not observed by 

 Behre) and not as in D. hinata, at first nastically (carrying the glands 

 away from a direct path) and later tropistically, correcting the error. 



Behre, having pointed out such minor differences in behavior as 

 between different species, remarks that, since the nastic and tropic re- 

 sponses are influenced differently by different temperatures, as when 

 the nastic responses are arrested by a high temperature while the tro- 

 pistic are stimulated, such differences may account in part at least for 

 various behaviors. By and large, however, the various species act in 



the same way. 



Aggregation. — Darwin observed that, following stimulation, the 

 contents of the gland cells first and later of those of the pedicel, dis- 

 play changes in appearance due to a rearrangement of the protoplasm 

 and vacuole which he termed "aggregation." The total effect is suf- 

 ficient to be seen by the naked eye, if pigment is present, in the change 

 of color of the gland. In this way it is possible to follow the direction, 

 if not the extent of the movement of a stimulus. While Darwin's de- 

 scription of these changes was incorrect, they stimulated a great 

 amount of work directed toward their elucidation. Those who have 

 seen at Down House the tools Darwin worked with may well wonder 

 at the extent and acuteness of observation which characterize his work 

 in this particular. Taken with the general state of the knowledge of 

 the cell in his day, the observations of Darwin are the more sur- 

 prising. 



Darwin gives his observations as follows: "If .... . tentacles that 

 have never been excited or become inflected be examined, the cells 

 forming the pedicels are seen to be filled with a homogeneous purple 



fluid. The walls are Hned by a layer of protoplasm ". " If a 



tentacle is examined some hours after a gland has been excited by re- 

 peated touches, or by an organic or inorganic particle placed on it, or 

 by the absorption of certain fluids, it presents a wholly changed ap- 

 pearance. The cells, instead of being filled with a homogeneous purple 

 fluid, now contain variously shaped masses of purple matter suspended 



in a colorless fluid By whatever cause the process may have 



been excited, it commences with the glands, and then travels down the 

 tentacles The Httle masses of aggregated matter are of the 



