Cucurbita maxima and G. Pejpo. 49 



ally be taken at from 8 cm when they first emerge from the bud 

 condition, to 35 cm when activity ceases. 



At first rolled up compactly as they come from the bud, 

 with the coils turned inward, the arms gradually extend to 

 their full length, and, within two days, activity begins in the 

 central arm while those which are lateral may yet be loosely 

 coiled. After motion once commences, the order of activity is 

 from the center outward, until all are involved. In this we sec 

 one of those curiously interesting provisions of nature for the 

 accomplishment of her plans. If all the tendril arms were of 

 the same length, or, more important, became equally active at 

 the same time, the express purpose for which they were pro- 

 vided, would fail of accomplishment in nine cases out of ten. 

 As it is, their activity extends over a considerable period, and 

 the first one in motion may have grasped an object, or, failing, 

 have become hard and inactive, long before the last gets fairly 

 in motion. It is the function of the tendril to draw the vine to 

 a secure and elastic support. By the succession of activity 

 here exhibited, one arm after another is enabled to grasp the 

 object of support and gradually draw the vine up to a secure 

 position ; whereas, by a simultaneous activity of all, a few only 

 might gain hold, or, if ail, only the last one or two would 

 bear all the strain, and the vine would remain at a greater dis- 

 tance from the point of support. 



Histology of the Tendril. 



In its histological aspects, the tendril of the squash vine pre- 

 sents a most interesting study, and throws much light upon 

 the cause of the movement; indeed, it is to evidence of this 

 character that we must chiefly look for a true solution of this 

 question. "We shall consider this part of our discussion under 

 two heads: (a.) Structure and peculiarity of component tissues 

 in their mutual relations, and (&.) Continuity of protoplasm. 



(a) Transverse sections of the tendril display the form and 

 general structure which is shown in fig. 3. From this it will 

 be seen that within the fundamental structure there are seven 

 fibro-vascular bundles, the largest of which are along the lower 

 side of the section and therefore traverse the lower region of 

 the tendril arm through its entire length. A more detailed 

 examination discloses several important facts. Directly be- 

 neath the continuous epidermis of one row of cells, there is a 

 somewhat thick layer of collenchyma tissue (fig. 3 a), extend- 

 ing completely round the tendril with the exception of three 

 regions where its continuity is fully interrupted by paren- 

 chyma tissue (fig. 3 b). These areas of interruption are found 

 to occupy the same relative positions in all squash tendrils ; 



Am. Joub. Sci. — Third Series, Vol. XXXI, No. 181. — Jan., 1886. 

 4 



