Chapter X 



— 97 



Duality of the Ghondriome 



Theory of the author:- From the series of facts which we have 

 just related, however, there arises the idea that the chondriosomes 

 of cells of the meristem do not all have the same significance, al- 

 though morphologically and histochemically similar. One is led 

 to think that the chondriome of embryonic cells in phanerogams, 

 although appearing homogeneous, is composed of two categories of 

 chondriosomes, maintaining their individuality throughout cellular 

 development. One of these categories corresponds to the plastids 

 and may take on much larger dimensions during the course of 

 development, by virtue of its active elaborative power. The other 

 of these categories, which kept its original size after the plastids 

 had become differentiated and to which we have provisionally given 

 the name inactive chondriosomes, seems to have functions which 

 are as yet not definitely determined. 



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Fig. 64 (left). — Chondriome in (1-4) diflferentiated colorless root par- 

 enchyma of Athyrium Filix-femina and in (5, 6) frog's liver. Regaud's 

 method. (After Mangenot and Emberger). 



Fig. 65 (right). — Detail of chondriome in (A) Saprolegnia and in (B) 

 epidermis of tulip perianth. X 3000. Regaud's method. 



These two categories have the same shape in the phanerogams 

 and it is almost always impossible to tell them apart in the meri- 

 stems and usually, also, even in mature cells which do not have 

 chlorophyll. They are, however, always perfectly distinct in some 

 lower plants (bryophytes, algae) in which chlorophyll is present 

 in all stages of development. 



Thus considered, the plastids are not differentiated chondrio- 

 somes; they are a special type of chondriosomes. In fact, when 

 the life history of the chondriosomes is followed in the phanero- 

 gams, one is struck by the chondriosomal characteristics which the 

 plastids always maintain. The amyloplasts are usually typical 

 chondriosomes and are only occasionally a little thicker than the 

 other elements of the chondriome. They are not actually distin- 

 guishable from the inactive chondriosomes coexistent with them, 

 until they become chloroplasts. In this case they appear as thick- 

 ened bodies which, in the last analysis, are only hypertrophied chon- 

 driosomes containing chlorophyll. As for the variations in plas- 

 tidial shape, we do not yet know whether they are caused by a 

 growth of these elements or merely by imbibition. 



