Francis E. Lloyd —186— Carnivorous Plants 



element is absent from the outer epidermis region. There is a total 

 absence of palisade tissue, a feature common to many carnivorous 

 plants, as Schmid showed. The parenchyma cells are elongated in 

 different degrees according to position. Below the chief vascular 

 strands in the midrib their long axes run lengthwise, above at right 

 angles to it and here are shorter. Those of the lateral regions run 

 up into the two lobes, and here they attain their greater longitu- 

 dinal dimensions, the largest, in the middle, being the longest. Ap- 

 proaching the margins, they become shorter and, as Munk points 

 out, are shortest, though not round, at the base of the ciha, length- 

 ening again in the cilia themselves. The intercellular spaces are 

 large and extensive, and while the protoplasm is very tenuous, chlor- 

 oplasts are present and much starch may occur, as Brown pointed 



out. 



Physiology. — If the question is asked how the structure just de- 

 scribed is related to the movement of the lobes, the answer is indicated 

 by comparing it with that of the lobes of very small traps found 

 in seedUngs, and with those of Aldrovanda. They all show the same 

 capacity for movement, whether the parenchyma consists of one 

 course of cells only {Aldrovanda) or of a few, as in seedlings traps. 

 The evidence indicates that the seat of movement resides in the 

 epidermis first of all. Further complication of structure is connected 

 with the mechanical strength of the lobes naturally greater in the 

 massive leaves of adult Dionaea plants. That is, the machine as 

 such is stronger (involving parenchyma cells) and can exert more 

 energy in the last, without any difference in the seat or directions 

 of movement. All movement occurs in the lobes and, as Brown 

 showed, none in the midrib, which is therefore not a hinge in any 

 sense. This is indicated in the diagram, borrowed from Ashida, shown 

 in i8 — 4a, though this does not indicate the extreme possibilities 

 of closure, better shown in iS — 46. 



The stimulus leading to action. — In nature the walking of an insect 

 across a lobe of the trap almost inevitably results in the disturbance of 

 the sensitive hairs, ensuring the prompt closure of the trap. This 

 Curtis (1834) clearly observed. Ellis (1770) had thought the move- 

 ment as following irritation of the glands by the feet of the prey, and 

 Broussonet (1784) believed that it was due to the loss of turgidity 

 caused by the pricking of the surface by insects. But from the time 

 of Curtis it was supposed that it was necessary only to touch a hair 

 to bring about closure, until the work of Burdon-S Anderson demon- 

 strated the fact of summation of stimuh. Macfarlant: found inde- 

 pendently that under usual circumstances (temperature is important) 

 in order to effect closure of the trap, it requires two stimuh, either by 

 touching the same trigger hair twice, or any two different ones with an 

 interval of time neither too short (about 0.75 sec.) nor too long (oyer 

 20 sec). This was in 1892. Previous observers, with the exception 

 above noted, had failed to notice this behavior, very obvious when 

 once seen. For example, Darwin says: "It is sufficient to touch any 

 one of the six filaments to cause both lobes to close . . . ," but observed 

 that an extremely delicate stimulus might be inadequate. Darwin 

 does remark, however, that " on another occasion two or three touches 



