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 oceurrence—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 
@ any trace of structure and crowded together 
3) in the substance of the plastid till they are 
almost in contact with each other (fig. 107). 
a pica atgeci The deposition is due to the protoplasm or 
Bopresor Caro. ‘stroma of the plastid, and does not depend 
Ropiasts. x 250. in any way 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 
