366 University of California Publications in Botany [Vol. 5 



2, c) is the chlorophyl-bearing region of the cortex (fig. 2, f), such 

 as occurs in Nicotiana, but in this case the tissue continues in the 

 pedicel distal to the groove. Beneath this chlorophyl-bearing tissue 

 is a layer of M'ell-developed collenchyma (fig. 2, g) which however 

 does not continue in the pedicel distal to the groove. The separation 

 layer (fig. 2, d) consists of three to six tiers of cells and is located 

 in a plane with the groove, differing in this respect from Nicotiana, 

 where it is located a short distance distal to the groove. Correspond- 

 ing to the condition in Nicoticma, the chief characteristic of the separa 

 tion cells is their small size, spherical outline and active physiological 

 condition. 



c. OTHER GENERA OF THE SOLANACEAE 



The condition of the pedicel, so far as the histology of the separa- 

 tion zone is concerned, was examined in several other species, a list 

 of which is given below : 



Solanum jasminioides Cestrum fasciculatum 



Solanum tuberosum Iochroma tuberosa 



Solanum verbascifolium Datura sanguineum 



Solanum umbelliferum Salpichrora rhomboidea 



Solanum nigrum Petunia hybrida 



Solanum marginatum Salpiglossis sinuata 



Lyeium australis 



The general condition of the pedicel of Datura sanguineum and 

 Petunia hybrida is worth describing in some detail. The tissues of 

 plants of D. sanguineum are more or less herbaceous in nature, large- 

 celled and somewhat succulent throughout. The chlorophyl-bearing 

 tissue which, in striking contrast with the condition in Nicotiana. and 

 Lycopersicum (figs. 1 and 2), is continuous over the separation zone, 

 is composed of two rows of small, spherical cells just beneath the 

 epidermis. Except for a layer of collenchyma, whose much elongated 

 cells extend the entire length of the pedicel and thus continue the col- 

 lenchyma through the separation layer, the cortex and pith are com- 

 posed of more or less isodiametric, thin-walled cells. Floral abscission 

 is as common in this species as it is in Nicotiana. The flowers are 

 very large and furnish excellent material for a study of the cytology 

 of abscission. Unfortunately not a sufficient number of flowers could 

 be obtained to make possible any detailed study of this genus. It was 

 noticed, however, that there is no region of small cells at the base of 

 the pedicel within which separation occurs and that the separation 

 cells are identical in size and shape with those on either side among 



