STRUCTURAL ELEMENTS OF THE CYTOPLASM. 183 



granules or droplets occurring in many animal cells, and they 

 have in all probability only secondary interest for purposes of a 

 generalized understanding of cytoplasmic structure. In my 

 first two reports ('260,, &) I called these platelets the "sphero- 

 somes" after the terminology of the Dangeards, and at first 

 suggested their homology with the "inactive chondriome" of 

 Guilliermond. Extended study of other classes of formed bodies 

 in the plant cell has, however, convinced me that such an 

 identification is impossible. These platelets are something new, 

 and certainly have nothing to do with Guilliermond's chondrio- 

 somal granules, as will appear more clearly in a succeeding 

 section. 



There is, finally, nothing about these platelets in root-tip cells 

 to furnish a critical demonstration of their status in the plant 

 cell. Their regular response to the Golgi apparatus methods 

 and their striking similarity to the scattered Golgi bodies of 

 many animal cells, suggests their homology with the animal 

 Golgi apparatus. Indeed, as will be indicated later, this is 

 probably more than a mere matter of coincidence, but for the 

 moment I wish merely to emphasize the lack of any conclusive 

 evidence as to their nature so far as such evidence might be 

 furnished by observations on root-tips. 



The Plastidome. This comprises a group of formed bodies 

 which occur generally in plant cells, appearing in older meristem 

 and more differentiated plant cells as centers for starch pro- 

 duction, deposit or storage the familiar plastids of various 

 kinds. In the earliest meristem, the forerunners of the plastids 

 are already present and may be called, in general, proplastids. 

 I have found thus far no evidence whatever in root-tips that the 

 plastidome ever has any relation to other cellular components, 

 and everything indicates that the proplastids constitute an 

 independent group of materials whose sole function is the 

 production of plastids in the more differentiated cells of the 

 plant. In root-tip cells the proplastids possess in general an 

 elongate, thread or rod-like shape (Figs. 2 and 3). They may 

 be blackened by osmic acid, especially in Vicia, but are probably 

 best demonstrated in Benda preparations, occasionally, as in the 

 hyacinth, with acid fuchsin. Every step in the gradual dep- 



