224 VEGETABLE PHYSIOLOGY 



the carbohydrate from the travelling to the storage forms, 

 and vice versa. 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 



