Guilliermond - Atkinson — 106 



Cytoplasm 



of granules, rods or chondrioconts, are able to change from one of 

 these forms to the next, and are characterized by a number of well 

 determined physical and chemical properties. The theory of the 

 duality of the chondriosomes has been remarkably confirmed by a 

 study of the life history of the chondriome throughout the plant 

 kingdom and is particularly well supported by the investigations 

 of Mangenot and Emberger. 



Development of chondriosomes and plastids among the plant 

 groups:- Emberger (1920-23), in investigating the pteridophytes 

 (Figs. 71-74), found that the egg cell in the ferns contains a chon- 

 driome exactly like that in the animal cells, in which chondriome it 

 is not possible to distinguish the plastids from other chondriosomes. 

 However, in those prothallial cells from which the egg cell is de- 

 rived there are both large chloroplasts and small chondriosomes. As 

 these cells differentiate in the course of the formation of the egg, 

 Emberger has shown that their chloroplasts lose chlorophyll and 



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Fig. 75 (left). — Selaginella Kraussiana. 1, vegetative tip of the 

 stem, each cell containing chondriosomes (C) and a slightly larger 

 plastid (P) appressed to the nucleus. 2, Diagram of developing 

 plastid during cellular differentiation. (After Emberger) . 



Fig. 76 (right). — Selaginella Kraussiana. Plastid (P) in living 

 parenchyma cell of the stem. (After Emberger). 



at the same time diminish progressively in volume, with the result 

 that they take on, little by little, the appearance of small elements 

 which it becomes impossible to distinguish from the chondriosomes. 

 The same phenomena occur in the formation of the antherozoids. 

 The fertilized egg resulting from the fusion of these cells shows, 

 therefore, a homogeneous chondriome. In the embryo, some of the 

 elements of this chondriome differentiate anew. In the leaves they 

 become chloroplasts, in the stem and root they become large chon- 

 drioconts which represent the starch-forming plastids. 



In the epidermal cells of leaves which will produce sporangia, 

 both chloroplasts and inactive chondriosomes are encountered. In 

 the young sporangia, however, the chloroplasts again lose their 

 chlorophyll and appear as typical chondriosomes, indistinguishable 

 from the inactive chondriosomes. From the time that the spore 

 begins germination, these typical chondriosomes grow larger, be- 

 come impregnated with chlorophyll and take on again the character 

 of chloroplasts. 



