228 VEGETABLE PHYSIOLOGY 
they are only intended to compensate for regular or acci- 
dental 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 
reservoirs 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 
p) in the substance of the plastid till they are 
almost in contact with each other (fig. 107). 
The deposition is due to the protoplasm or 
Pres or Srancu’ stroma of the plastid, and does not depend 
opis or CuLo- in any way upon the colouring matter, the 
epee ea 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 
