218 VEGETABLE PHYSIOLOGY 
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 
interference 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 instead of being removed by the slow pro- 
cess of diffusion. 
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 re- 
servoirs 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 modification 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 process by 
which they travel, we have seen, is mainly one of diffusion 
through the cell-walls, the latter being saturated with the 
