120 PULVINI OF COTYLEDONS. CHAP. II. 



same pulvinus and in different individuals. In the accompany- 

 ing figures, A and B (Fig. 64), we have views of the epidermis * 

 in the middle part of the petioles of two seedlings, in which the 

 pulvinus was for this species well developed. They offer a 

 striking contrast with the pulvinus of 0. rosea (see former 

 Fig. 63), or of 0. Valdiviana. With the seedlings, falsely called 

 0. tropceoloides, the cotyledons of which rise very little at night, 

 the small cells were still fewer in number and in parts formed 

 a single transverse row, and in other parts short longitudinal 

 rows of only two or three. Nevertheless they sufficed to attract 

 the eye, when the whole petiole was viewed as a transparent 

 object beneath the microscope. In these seedlings there could 

 hardly be a doubt that the pulvinus was becoming rudimentary 

 and tending to disappear; and this accounts for its great 

 variability in structure and function. 



In the following Table some measurements of the cells in 

 fairly well-developed pulvini of 0. corniculata are given : 



Seedling 1 day old, with cotyledon 2'3 mm. in length. 



Divisions of 

 Micrometer.f 



Average length of cells of pulvinus 6 to 7 



Length of longest cell below the pulvinus 13 



Length of longest cell above the pulvinus 20 



Seedling 5 d <ys old, cotyledon 3'1 mm. in length, wi!h the pulvinus 

 quite distinct. 



Average length of cells of pulvinus 6 



Length of longest cell below the pnlvinus 22 



Length of longest cell above the pulvinus 40 



Seedling 8 days old, cotyledon 5 mm. in length, with a true leaf 

 formed but not yet expanded, 



Average length of cells of pulvinus 9 



Length of longest cell below the pulvinus 44 



Length of longest cell above the pulvinus 70 



Seedling 13 days old, coti/ledon 4*5 mm. in length, with a smill 

 true leaf fully developed. 



Average length of cells of pulvinus 7 



Length of longest cell below the pulvinus 30 



Length of longest cell above the pulvinus CO 



* Longitudinal sections show pulvinus. 



that the forms of the epidermic f Each division equalled '003 



cells may be taken as a fair repre- mm. 

 sentation of those constituting the 



