224 



BOTANY 



Other substances similar to diastase, and also capable of transforming starch 

 into dextrin, maltose or glucose, are widely distributed throughout the vegetable 

 kingdom, and are classed together as diastatic ferments. They are especially 

 abundant in starchy germinating seeds, as well as in tubers and bulbs, in leaves 

 and young shoots. They have also been found, strange to say, in organs where 

 there was no starch for them to act upon. The diastatic transformation and dis- 

 solution of the starch is accomplished in a peculiar manner. The starch grain 

 is not dissolved as a homogeneous crystal, uniformly from the surface imv.-ir IN 

 but becomes corroded by narrow canals, until it is finally completely disorganised, 

 and falls into small pieces (Fig. 201). 



The complete transformation of the starch formed in the chloro- 

 phyll corpuscles during the day, takes place, as a rule, at night ; for in 



the daytime the action of the 

 diastatic ferment is counter- 

 balanced by the formation of 

 s new starch. The glucose 

 which is thus produced in the 

 leaves passes out of the meso- 

 phyll cells into the elongated 

 cells of the vascular bundle- 

 sheaths and from them into 

 ; the phloem. The glucose 

 |* and maltose are transferred 

 through the leaf-stalks into 

 the stem. Thence they are 

 conveyed to the young shoots 

 and buds or carried down to 

 the roots ; in short, they are 

 finally transported to places where they are required for the nutrition of 

 the plant. The glucose and maltose often become converted into other 

 carbohydrates, particularly into starch, during their passage from one 

 organ to another. Starch thus formed from other carbohydrates, and 

 not directly by assimilation, is often referred to as TRANSITORY STARCH, 

 and is iisually distinguishable by the smaller size of the grains. 



For the purpose not of transport but of protection against cold starch i.s some- 

 times transformed into sugar (sweetening of potatoes) or oil (in the cortex and 

 sometimes the wood of trees) ( 45 ). 



The Storage of Reserve Material 



All the products of assimilation are not at once consumed. In 

 spite of this, however, assimilation is continued, and the surplus 

 products beyond the requirements of immediate consumption are re- 

 moved from the place of formation and accumulated as RESERVE 

 MATERIAL for future use. In our herbs, bushes, and trees, as the 

 yearly growth and consequent consumption cease towards the end 

 of each vegetative period, and as the assimilating organs have by 



Fi<:. -'01. Different stages of corrosion shown by tlir 

 starch grains of germinating Barley. 



