Chapter X 



DUALITY OF THE CHONDRIOME 



The first data obtained in our laboratory by Emberger and 

 Mangenot on the pteridophytes and the algae as well as the 

 very meticulous study of the development of the chondriome in 

 certain phanerogams, notably in the bud of Elodea canadensis and 

 in the root of Cucurbita Pepo, led us, as early as 1920, to formu- 

 late a new theory which removes all the difficulties and accords 

 with all the facts drawn from the development of plastids in the 

 plant kingdom. 



It has been seen that among the elements which constitute the 

 chondriome in meristematic cells of the bud of Elodea canadensis, 

 it is possible to distinguish between the chondrioconts which be- 

 come chloroplasts during cellular differentiation, and the granular 

 mitochondria which do not participate in this phenomenon but 

 elongate into rods and later into chondrioconts. Now it has been 

 known for a long time that chloroplasts have the ability to divide. 

 Our work has shown that it is only by this process that they in- 

 crease in numbers and that in differentiated cells the chondrio- 

 somes which persist along with the plastids are incapable of becom- 

 ing chloroplasts. This shows therefore that the two categories 

 of elements which constitute the chondriome of cells of the meri- 

 stem develop separately and seem independent, one of the other. 



The study of the development in the chondriome in the root of 

 Cucurbita (Figs. 59, 61) will furnish a similar example. Here again, 

 there is observed in the cells of the meristem a chondriome com- 

 posed of two categories of elements : chondrioconts and mitochon- 

 dria or short rods. If, in the course of cellular differentiation, the 

 development of these elements is followed, it is seen that in the cen- 

 tral cylinder, where elaboration of starch is not very active, the 

 appearance of the chondriome does not change and one witnesses the 

 production of small starch grains only within the chondrioconts. In 

 the cortex, on the contrary, the chondrioconts undergo a consider- 

 able thickening and may be subdivided into rods or granules. The 

 other chondriosomes keep their original size but sometimes take the 

 form of chondrioconts which differ from the other chondrioconts 

 by being thin. Our first impression is that there exist at this mo- 

 ment in the cells, two categories of chondriosomes, the one consist- 

 ing of large chondriosomes, the other of little ones. The large 

 chondriosomes represent the amyloplasts. At certain periods they 

 are the seat of active elaboration of compound starch. Once having 

 reached maturity, the starch grain formed in the interior of the 

 larger chondriosomes considerably modifies the appearance of the 

 latter. The starch is seen as a large grain surrounded by a thin 

 mitochondrial layer. This layer is often prolonged as a tail, the 



