Guilliermond - Atkinson — 118 — Cytoplasm 



that there is in the plastid only a synthesizing diastase and that 

 the hydrolyzing diastase has its seat in the cytoplasm. The ex- 

 istence of diastase is, however, not necessary, if the hypotheses 

 are accepted as formulated by Nageotte and Devaux who con- 

 sider the plastids and chondriosomes as catalysts. 



It is known, moreover, that plastids in the embryo sac of Lilium 

 candidum may enclose protein crystalloids which are used as re- 

 serve products. Some experiments seem to indicate that the plas- 

 tids have the ability to accumulate proteins and it is even possible 

 that they may be very important synthesizing ceriters (Ullrich, 

 Granick, etc.). Recently Volkonsky seems definitely to have 

 furnished proof that the reticulate leucoplast of Polytoma uvella 

 undergoes considerable variations in volume depending on the na- 

 ture of the nutriment furnished it. It expands greatly in media 

 rich in assimilable nitrogen. The leucoplast seems, therefore, to 

 be the region of the cell to which nitrogenous nutrients most readily 

 go, especially the amino acids, which are there transformed into 

 more complex products. This phenomenon is to be considered in 

 connection with the observations of Noel on chondriosomes in 

 livers of mammals, and seems to confirm the hypothesis of Robert- 

 son-Marston, of which more will be said later. Yet Volkonsky 

 says that this synthesis does not go beyond polypeptides and that 

 the formation of proteins is completed in the vacuoles. 



It is seen that, in reality, we are still very insuflniciently in- 

 formed on the role of plastids. The close relationship of the plas- 

 tids and chondriosomes leads us to suppose that the two categories 

 of elements must have a single function which is very general 

 and that the function manifested morphologically by the plastids 

 is only a special example of it. Thus, while admitting with the 

 majority of cytologists that the chondriosomes have an important 

 role in metabolism, we can, at the same time, examine the various 

 hypotheses which have been proposed to explain the role of plas- 

 tids and that of chondriosomes and which may apply to both 

 categories of elements. 



Purely for historical interest, the theory formulated in France 

 by PoRTiER (1919), then in America by Wallin (1922) may first 

 be mentioned. This theory held that the chondriosomes and plas- 

 tids represent symbiotic bacteria which are found present in all 

 cells and by means of which all syntheses take place in the 

 cell. It was based solely on the morphological resemblance of the 

 chondriosomes to bacteria and on the fact that with mitochondrial 

 technique the symbiotic bacteria which are encountered in certain 

 cells, notably those in the bacteria-containing root nodules of the 

 legumes, stain like the chondriosomes. The theory is untenable, 

 for even if it is true that the symbiotic bacteria stain as the chon- 

 driosomes do by these techniques, it signifies nothing since these 

 stains are not specific and since symbiotic bacteria show histo- 

 chemical behavior which makes it impossible to confuse them with 

 chondriosomes (resistance to alcohol, acetic acid, etc.). This the- 

 ory, successfully opposed by Laguesse, Regaud, Cowdry and Olit- 



