238 BOTANY part i 



Leguminosae (15 g. arc present in a litre of sap from bean seedlings) ; they are 

 replaced in Cruciferae and Cucurbitaceae by glutaniin, while in the Coni ferae a 

 hexon-base, arginin, appears to play the same part. The syntheses proceed still 

 farther in light, when proteid may again be formed from the products of decom- 

 position of albumen and from amides. 



Albumen occurs in the storage places for reserve materials partly 

 in a crystalline and partly in an amorphous form. The crystals occur 

 free in the cytoplasm, nucleus, or in the chromatophores ; in seeds 

 they are found especially in the aleurone grains, where they are 

 associated with globoids. The latter then contain Ca, Mg, and 

 phosphoric acid in an organic compound (cf. p. 66). 



B. Transport of the Mobilised Reserve Materials 



When the reserve materials have been brought by the aid of the 

 proper enzymes into the soluble form, or have been transfoi^med into 

 substances with smaller molecules, they are capable of being 

 transported ; we may speak of them as being mobilised. Their 

 movements are governed by the general principles of translocation of 

 substances discussed on page 186. It is especially necessary that a 

 diffusion current should be established and maintained. This is brought 

 about by the active growth of cells at a greater or less distance from 

 the place of storage of the reserve material. As long as this lasts 

 each molecule on its arrival at the place of growth is promptly 

 transformed {e.g. sugar into starch or cellulose), and thus room is made 

 for the molecules that follow. A diffusion current can also be artificially 

 established where a storage structure under proper conditions is 

 placed in relation on one side with a large amount of water. It is thus 

 possible to bring about an emptying of seeds, bulbs, etc. 



When substances have to be transported for considerable distances, 

 the movement of diffusion since it goes on slowly, is replaced by 

 movement in mass. Thus in spring the reserve materials deposited 

 in the wood of our trees are carried up by the ascending current 

 of water in these vessels ; at this season the fluid in the vessels con- 

 tains abundant glucose. In the other direction a stream of mobilised 

 reserve material can pass downwards from the foliage leaves by way 

 of the sieve tubes. While, however, the mechanical causes of the 

 transpiration stream are at least partially understood, so far as they 

 depend upon the evaporation of water we do not know the forces 

 concerned in movements in mass in the sieve-tubes. 



The foliage leaves accumulate during the day large quantities of starch (p. 219) 

 wliicii under favourable conditions pass in a niglit by way of the leaf-stalk to the 

 stem. If tlie sieve-tubes of one half of the petiole are cut across, the stream of 

 carbohydrates is arrested and the corresponding half of the leaf remains full of 

 starch. In stems also when these are "ringed," i.e. when a complete ring of the 

 riud is removed, au accunuilation of reserve materials is observed at the upper 



