204 



BOTANY 



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 dissolution of the starch is accomplished in a 

 peculiar manner. The starch grain is not dissolved as a homogeneous crystal, 

 uniformly from the surface inwards, but becomes corroded by narrow canals, until 

 it is finally completely disorganised and falls into small pieces (Fig. 184). 



The transformation of the starch formed in the chlorophyll corpuscles 

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



action of the diastatic ferment 

 is weaker, and is also counter- 

 balanced by the formation of 

 new starch. The glucose 

 which is thus produced in the 

 leaves passes out of the 

 mesophyll cells into the elon- 

 gated cells of the vascular 

 bundle-sheaths. The glucose 

 and maltose are transferred 

 in these conducting sheaths 

 through the leaf- stalks into 

 the stem. Thence they are 



Fig. 184.— Different stages of corrosion shown by the conveyed to the young shoots 

 starch grains of germinating Barley. ^ budg ^ ^^ d()wn 



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 during 

 their passage from one organ to another, particularly into starch. 

 Starch thus formed from other carbohydrates, and not directly by 

 assimilation, is often referred to as transitory starch, and is usually 

 distinguishable by the smaller size of the grains. At the points of 

 consumption these carbohydrates are again converted into glucose, in 

 which condition alone they seem adapted for direct nutrition. 





'<■?< 



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 accu- 

 mulated as reserve MATERIAL for future use. Large amounts of such 

 reserve material are accumulated by the American Agave during many 

 periods of vegetation, to be finally expended in nourishing the immense 

 inflorescence with its hundreds of flowers and fruits. In our herbs, 

 bushes, and trees, as the yearly growth and consequent consumption 

 cease at the end of each vegetative period, and as the assimilating 

 organs have by that time attained their greatest expansion and 

 efficiency, the surplus of reserve material is the greatest at the close of 



