Guilliermond - Atkinson 



— 72 — 



Cytoplasm 



that the great majority of cytologists are at present in agreement 

 in recognizing that the plastids of Schimper are derived from 

 elements presenting the same forms as those of the chondriosomes. 

 The life history of the chondriosome in phanerogams will now 

 be studied in detail by first following the formation of chloroplasts. 

 As the phenomena are the same in all buds, it is sufficient to 

 choose a single example. The most favorable, because of the dis- 

 position of foliar primordia, is the bud of Elodea canadensis, first 

 investigated by Lewitsky. Afterward, it was the object of inten- 

 sive study for us and our reports were confirmed by Friedrichs. 

 If a longitudinal section of a bud of Elodea canadensis be ex- 

 amined after being fixed by Regaud's method 

 \ . , -2is« ^ ,^^ (fixation by a mixture of potassium bichromate 



'l{"ly^<^^^'' ^^^ formaldehyde, and staining with iron 

 Cv^V<-==Crr haematoxylin), there may be observed in the 



meristem of the stem and in the youngest foliar 

 primordia, a chondriome exactly like that of 

 many animal cells, composed of a mixture of 

 chondriosomes and granular mitochondria. 

 These elements have a diameter of about 

 0.5-1/x. (Fig. 36). 



By following successively developed foliar 

 primordia, there may be seen with the great- 

 est accuracy, all the developmental stages of 

 the chondriome and it may be observed that 

 the chondrioconts differentiate into chloro- 



plasts. The differentiation, manifested by a 



N^H." / -i^ thickening of the chondrioconts, begins in 

 t> ^i!S^S>'=k Vx- those foliar primordia which are about 160/i 



long. In those measuring about 200/i in length, 

 the chondrioconts form little swellings on their 

 long axes in which a small starch grain is 

 sometimes elaborated. As this grain is not 

 stained by iron haematoxylin, it looks like a 

 vesicle. Starch grains thus formed are only 

 transitory and soon disappear. The swellings 

 then gradually separate by rupture of the slen- 

 der portions between them. They increase in volume and, in ma- 

 ture cells, take on the appearance of large, rounded or ovoid, chloro- 

 plasts about 4-8)11 in diameter. These are distinguished from the 

 chondrioconts, from which they arose, by the modification which 

 they have undergone in their chemical qualities which gives them 

 a special resistance. They are preserved by all the fixatives which 

 destroy the chondriosomes. Henceforth these chloroplasts often 

 elaborate large starch grains. 



During the differentiation just described, the granular mito- 

 chondria elongate first into rods then, in mature cells, generally 

 become typical chondrioconts. 



In the axil of each leaf primordium there is found, as is known, 

 a small scale made up of a group of cells in which there is no pro- 



Fio. 35. — A compari- 

 son (A) of the chondri- 

 ome of the vegetative 

 point of Elodea canaden- 

 eis with (B) that of the 

 liver of a mouse. Re- 

 eaud's method. X 3,000. 



