224 VEGETABLE PHYSIOLOGY 
the carbohydrate from the travelling to the storage forms, 
and vice versd. It is very usual to find temporary accumula- 
tions of starch in the neighbourhood of a growing region. 
Grains of starch are of frequent occurrence in different 
parts of the bast, and particularly in the bundle-sheaths of 
certain regions. The explanation of their appearance there 
is simple; they are generally indications of such an inter- 
ference with the supply and the demand as we have described. 
A checking of the demand by a cessation of the vigour of 
growth or nutrition is attended by an over-accumulation 
of the sugar, which is speedily changed into a storage form. 
The transport of proteins follows the same course; the 
amino- or amido-acids are the travelling forms, and are 
conducted by the same forces to the growing points, or to 
reservoirs where accumulation of proteins takes place. 
Their deposition in storage forms along the pathway can 
also be detected, though these are not so widespread as 
those of carbohydrates. They can be observed generally in 
the sieve-tubes of the bast, which contain a curious modifica- 
tion of protoplasm in which protein as such is present. It 
was formerly held that the sieve-tubes conduct protein as 
such along the vascular bundles. Though there is not a 
very great improbability that such bodies may pass from 
cell to cell of the sieve-tube, on account of the protoplasmic 
or quasi-protoplasmic threads which extend throughout the 
openings of the sieve-plates, yet this method of transport 
must be necessarily very slow and subject to much hindrance. 
It seems more probable that the proteins in these vessels 
are constructed there from the amino-acids which reach 
them, and are to be regarded as temporary stores, like the 
starch grains already alluded to as being formed in different 
parts of the translocatory tract. 
We have spoken of the bast as forming the pathway of 
the translocation of nutritive material or of the different 
food-stuffs which have been manufactured. The protoplas- 
mic threads that extend through the openings of the sieve- 
plates no doubt afford facilities of passage. It must not 
