120 PULVINI OF COTYLEDONS. CHAP. 11. 



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. Valdivwna. With the seedlings, falsely called 

 0. tropceoloi/les, 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 



Seedlimj 5 diys old, cotyledon :-M mm. in length, with the pulmnus 

 quite distinct. 



Average length of cells of pulvinus 6 



Length of longest cell below the pulvinus 22 



Leng;h of longest cell above the pulvinus 40 



Seedling 8 days old, coti/ledon b mm. in length, with a true leaf 

 formed but not i/et expanded. 



Average length of cells of pulvinus 9 



Length of longest cell below the pulviuus 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 pulviuus tO 



* Longitudinal sections show pulvinus. 



that the forms of the epidermic f Each division equalled '008 



cells raay ho taken as a fair repre- mm. 

 entutiDii of those constituting the 



