54 THE POPULAR SCIENCE MONTHLY. 



glands are stimulated, and the extreme' marginal tentacles become 

 inflected, tlie motor impulse is transmitted across half the diameter 

 of the disk. It passes not along the vascular system, but through 

 the cellular tissue, traveling more rapidly and easily in a longitudinal 

 than in a transverse line, probably for the reason that the cells are 

 elongated longitudinally, and some obstruction is encountered at 

 each cell-wall through which the motor impulse must pass. 



A molecular change of the protoplasm within the cells, to which 

 Mr. Darwin has given the name of aggregation, precedes and accom- 

 panies all motion. When a leaf which has not been excited or in- 

 flected is examined, the cells forming the pedicels are seen to be filled 

 with an homogeneous purple fluid. If the tentacle be examined some 

 hours after having been excited, the purple matter is found to be 

 aggregated into masses of various shapes suspended in a colorless 

 fluid. The change begins within the glands and travels downward, 

 being arrested for a short time at each cell-wall ; the aggregated 

 masses perpetually changing form, separating and uniting. After 

 the cause of the excitement has been removed, and the tentacles 

 have reexpanded, the colored masses of protoj^lasm are redissolved, 

 and tlie purple fluid again becomes homogeneous and transparent. 

 TJjis process of aggregation is not dependent upon the inflection of 

 the tentacles or increased secretion of the glands a most remark- 

 able feature of the phenomenon being that in the tentacles which are 

 inflected by an indii'ect irritation, conveyed by motor impulse from 

 other glands, some influence is sent up to the glands, as their secre- 

 tion is increased and becomes acid ; then the glands tljus excited 

 send back some other action, causing the protoplasm to aggregate in 

 cell beneath cell. There can actually be seen a molecular change pro- 

 ceeding, which may be somewhat similar to the molecular change 

 which is supposed to be sent from one end of a nerve to another when 

 sensation is felt. "We have here a reflex action, and the only known 

 case thereof in the vegetable kingdom. The rate at which the motor 

 impulse is transmitted is much slower than in animals. This fact, as 

 well as that of the motor impulse not being specially directed to cer- 

 tain points, are both, no doubt, due to the absence of nerves. Never- 

 theless, we perhaps see the prefigurement of the formation of nerves 

 in animals in the transmission of the motor imjjulse being much more 

 rapid down the confined space within the tentacles than elsewhere, 

 and somewhat more rapid in a longitudinal than in a transverse direc- 

 tion across the disk. 



Of course, there is not in this, or in the reflex action, any thing 

 comparable with the nervous systems of animals, and, as Mr. Darwin 

 says, " the greatest inferiority of all is the absence of a central 

 organ, able to receive impressions from all points, to transmit their 

 effects in any definite direction, to store them up and reproduce 

 them." That is to say, Drosera seems to be without even the pre- 



