Guilliermond - Atkinson — 100 — 



Cytoplasm 



Histochemical and histophysical characteristics of chondriosomes 

 and plastids:- We proceeded ourselves to make a comparative histo- 

 chemical study of the two chondriosomal categories in chlorophyll- 

 containing plants with respect to the chondriosomes of the Sapro- 

 legniaceae. In the latter, there exists only one category of 

 chondriosomes which can be unquestionably homologized with the 

 chondriosomes of animal cells as we have seen earlier in these pages. 

 This study consisted first of a comparative examination, made 

 as accurately as possible, of the chondriome of epidermal cells from 

 portions of a tulip perianth (white variety) and of the chondriome 

 of Saprolegnia, both of which are particularly favorable for ob- 

 servation of living material. (Figs. 65, 66). 



The living chondriome in these two different tissues has a sim- 

 ilar morphological appearance and refrac- 

 tivity. It is represented in the tulip by long, 

 thin, undulating and sometimes branching, 

 chondrioconts which correspond to the plas- 

 tids, and by the inactive chondriosomes in 

 the form of granules or short rods. In 

 Saprolegnia, except for the region at the tips 

 of the hyphae, the chondriome, as we have 

 seen, is formed exclusively of long and some- 

 times branched chondrioconts entirely sim- 

 ilar to the tulip plastids. Meyer, who had 

 observed them before the discovery of chon- 

 driosomes in the fungi of the same group, 

 did not hesitate to liken them to plastids. 

 These elements arise from mitochondria by 

 growth and elongation, just as do the tulip 

 plastids. It is in the mitochondrial form 

 that they appear in the extremities of the 

 hyphae of Saprolegnia and in epidermal 

 cells in perianth parts of very young tulip 

 flowers. 



This study was completed later by sim- 

 ilar observations which we made on epider- 

 mal cells from the leaves of Iris germanica 

 and especially on epidermal cells from the bulb scales of Allium 

 Cepa. In these bulb scales, the plastids and the chondriosomes 

 present the same forms. They are both composed of a mixture of 

 mitochondria, short rods and chondrioconts. As the plastids do 

 not elaborate starch, it is very difficult to tell the two categories of 

 elements apart. The plastids, however, are often recognizable 

 because they are slightly thicker than the chondriosomes and are 

 longer when they are in the chondriocont stage. We will therefore 

 review briefly here the principal results which we have obtained 

 from this comparative study and add those reported by other 

 authors. 



The two categories of chondriosomes, plastids and genuine 

 chondriosomes (Fr. chondriosomes proprement dits), of epidermal 



f f 

 {tf 

 ( I 



X B 



Fig. 68. — Epidermal cell 

 of Iris germanica. At right, 

 modifications in form ob- 

 served when a chondriocont 

 moves as from (A) to (B) 

 in the diagram at the left 

 where arrows indicate direc- 

 tion of current. 



