Chapter VIII 



— 75 — 



The Ghondriome (cont'd) 



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wards separate and then elaborate a grain of transitory starch. 

 It is not until this is absorbed that the swellings increase in vol- 

 ume and take on their characteristic appearance of large chloro- 

 plasts. 



The living root of Elodea does not lend itself to study. On the 

 other hand, Regaud's method brings out in the meristem a chondri- 

 ome entirely similar to that of the vegetative tip. During the 

 differentiation of tissues all that can be obsei'ved is that a certain 

 number of elements of the chondriome, especially the chondrioconts, 

 without modifying their form or chemical quality, elaborate little 

 starch grains along their long axes, but this elaboration is not very 

 active. When the root is exposed to light, on the contrary, there 

 are formed in the course of cell- 

 ular maturation and by differen- 

 tiation of a part of the chondrio- 

 somes, chloroplasts similar to 

 those in the stem and leaves. 



A study of the root of the 

 castor bean (Figs. 37, 38) is 

 more profitable and will serve as 

 an example here. The chondriome 

 of cells of the meristem is, here 

 also, composed of a mixture of 

 granules, rods and chondrio- 

 conts. In the central cylinder, a 

 part of these elements, especial- 

 ly the chondrioconts, elaborate 

 small starch grains directly. On 

 the long axis of the chondrio- 

 conts, there are seen to form small 

 vesiculate swellings occupied by 

 a sort of vacuole which corre- 

 sponds actually to a starch grain 



left colorless by Regaud's tech- starch by the chondrlocont-shaped amyloplasts 



nique. Soon, around this small 



starch grain, others are seen to appear which give a spongy ap- 

 pearance to the swellings and thus a compound starch grain is 

 produced. This increases in size little by little while remaining 

 surrounded by a thin mitochondrial layer prolonged to a sort of 

 tail, the remaining portion of the chondriocont. In the cells of 

 the cortex, on the contrary, some of the elements of the chondri- 

 ome differentiate by thickening slightly and it is not until after 

 this is accomplished that they elaborate starch as first described. 

 Thus, some of the elements of the chondriome elaborate starch 

 and play the role of amyloplasts either immediately, or after thick- 

 ening slightly. It is easy to obtain the characteristic reaction for 

 starch by treating the preparation obtained by Regaud's method 

 with the reagent iodine-potassium iodide. The chondriocont is 

 stained by the haematoxylin while the starch grain becomes yellow- 

 ish brown, due to the action of the xylol which turns yellow the 



Fig. 38. — 1,2,3A, the chondriome in the 

 castor bean root. 3B, in the bean root. 1. 

 portion of a parenchymatous cell of the 

 central cylinder showing the nucleus sur- 

 rounded by chondriosomes (C) and amylo- 

 plasts (A); 2, amyloplasts containing com- 

 pound starch (o) in a similar cell; 3, less 

 iiighly magnified stages in the formation of 



