234 VEGETABLE PHYSIOLOGY 



accidental intermittence in the translocatory stream to the 

 parts in question. The food is temporarily stored in the 

 ordinary parenchymatous cells or in the sheaths of the con- 

 ducting tissue, and no special arrangements are made to 

 receive it. It is often of accidental occurrence deposited 

 suddenly and gradually or rapidly removed. Such deposi- 

 tion and re-absorption form, indeed, one of the features of 

 the transporting mechanisms. 



We may now pass to the consideration of the forms in 

 which the different foods present themselves in these re- 

 servoirs of storage. It is not surprising that we find here 

 a great deal of variety, even in any particular class of food. 

 The more prolonged the stay in the reservoir, the more 

 complex usually is the structure which the nutritive 

 substance assumes. 



We may deal, in the first instance, with the stores of 

 carbohydrates. We have already noticed that in the 

 great majority of cases these take the form of starch. In 

 the chloroplasts in the leaf-cells the starch grains are 

 laid down as minute bodies, showing hardly 

 A any trace of structure and crowded together 



in the substance of the plastid till they are 

 almost in contact with each other (fig. 107). 

 FIG. 107. STABCH The deposition is due to the protoplasm or 

 BODIES OCHLO. stroma of the plastid, and does not depend 

 ROPLASTS. x 250. i n an y wav upon the colouring matter, the 

 presence of the latter influencing only the 

 other function of the chloroplast, the synthesis of sugar, 

 as we have already seen in a previous chapter. The process 

 is thus one of true secretion, and the deposition of the 

 starch originating at several centres in the plastid, several 

 granules are coincidently formed. The number, however, 

 is not constant. 



In the more permanent reservoirs of starch it usually 

 happens that the cells are so charged with the grains that 

 they appear to contain nothing else. Fig. 108 shows a 

 cell taken from the interior of a potato tuber. These 



