Guilliermond - Atkinson — 114 — Cytoplasm 



developing side by side without any genetic bond between them. 

 This is undeniable and cytologists are more and more inclined 

 today to admit it. There is only one point which still remains hy- 

 pothetical and this is the identification of plastids with chondrio- 

 somes which many cytologists still refuse to accept. In order to 

 settle the question definitely we should have to know more pre- 

 cisely the chemical constitution of these two categories of elements 

 and this is impossible in the present state of science. We should 

 also have to obtain information on the phylogeny of plastids and 

 chondriosomes which now escapes us. That which is certain is 

 that the chondriosomes and plastids can only be regarded as very 

 closely allied formations. It is illogical to deny these incontestable 

 relationships as so many cytologists still do, for it is a much greater 

 assumption to consider them as essentially different formations 

 than it is to put them both together under the heading of chondrio- 

 somes. Also, our theory, which nothing has contradicted since we 

 formulated it nearly twenty-five years ago, seems to be the only 

 interpretation possible in the present state of knowledge. It has, 

 furthermore, the advantage of suggesting a series of working hy- 

 potheses, not only with respect to the role of the genuine chondrio- 

 somes which is at present almost completely unknown, but also 

 with respect to the physiological f unctionings of the plastids in the 

 elaboration of chlorophyll, their functioning in photosynthesis and 

 in the condensation of hexoses into starch. It is possible to imagine 

 that a day will come when the physico-chemical study of the cyto- 

 plasm will show us that the chondriosomes have a very general 

 function of which that manifested by the plastids is only one 

 specific part. 



Phylogenesis of chondriosomes and plastids:- Nothing is known 

 about the phylogenesis of these two categories, chondriosomes and 

 plastids, whose chemical constitutions are so closely allied. The 

 fungi, which many botanists consider to be derived from the algae, 

 show, however, no trace whatever of plastids. There is only one 

 line of chondriosomes in them. In the Cyanophyceae (p. 41), 

 which by reason of the primitive structure of their nucleus, may be 

 considered as the most inferior algae known, it is impossible, as 

 we have seen above, to detect the presence of chondriosomes and 

 of plastids. The chlorophyll is diffuse in the cytoplasm of these 

 algae. It has sometimes been thought that the lipoprotein sub- 

 stance of plastids and chondriosomes was also diffused in the cyto- 

 plasm. This, however, is only an hypothesis based on the absence 

 of plastids and on the fact that chlorophyll can hardlj^ have as sub- 

 stratum any other than a lipoprotein substance. In all flagellate 

 algae, another inferior group thought to be the common ancestors 

 of algae and protozoans, there exist very varied forms, some with 

 chlorophyll, some without. All contain chondriosomes (Chade- 

 FAUD). We have seen that in chlorophyll-containing forms the 

 plastids sometimes look like the chloroplasts of phanerogams 

 (Euglenas, Peridiniaceae) , sometimes appear as a single voluminous 



