CUCURBITA 



617 



of the tendril is subterete with a central hollow in its main 

 unbranched section. In the intermediate portions, it is more or 

 less polygonal, and the distal part is somewhat dorsiventrally 

 flattened. (Fig. 3xx, A, B.) Haberlandt (14) observed that 

 the tendrils are sensitive only on the abaxial side, which is usually 

 devoid of hairs. There are a few stomata which occur in other 

 sectors of the epidermis in a frequency of about 16 per sq. mm. 



Fig. 3x2.. A, diagrammatic transection of proximal portion of tendril showing distribution 

 of vascular bundles and mechanical tissue ; B, transection of distal portion in region of curva- 

 ture. The diagrams are oriented with adaxial surface uppermost. The epidermal cells of 

 abaxial surface contain sensory spots shown in C. These spots are underlain by tactile pits as 

 shown in transection of similar cells in D. The pit (j) may contain a small crystal of calcium 

 oxalate. In A and B, collenchyma is indicated by cross-hatching; sclerenchyma is lined; 

 and chlorenchyma is designated with chloroplasts. The phloem of bicollateral bundles is 

 stippled and xylem is black. (C and D, redrawn after Strasburger, Textbook of Botany.') 



The epidermis of the sensitive portion of the tendril is unlike 

 that of other regions in several respects. The cells are usually 

 smaller and the outer walls have little cuticle until after the 

 tendril is attached to a support, when they become thick and 

 heavily cutinized. Haberlandt found that the sense epithelia 

 on the sensitive side are located above a continuous wide band of 

 collenchyma. The sense cells are somewhat stretched; and, in 

 the center of each outer wall, there is a single sensitive spot or 

 papilla. (Fig. 32.1, C.) The interior of the papilla forms a 



