THE RESERVE MATERIALS OF PLANTS. 67 



peripheral layer of the seed in its young condition is 

 also supplied very fully with these local reservoirs. We 

 appear to have here a deposit laid down to supplement the 

 regular stream which is passing all about the plant by means 

 of the conducting tissue of the bast. It is doubtless derived 

 from the circulating supply, for if the latter be interrupted 

 by a section passing across the stem through its path, the 

 disappearance of the acid takes place from the bast tissues 

 below the wound some time before it does from the isolated 

 special cells of the cortex. 



From the work of Treub and of Guignard then it seems 

 increasingly probable that the glucosides are reserve 

 materials, and not simply bye-products or products of 

 excretion. Nor is it apparently only the sugar in them 

 which has a nutritive value, but the other products of their 

 decomposition have a particular part to play in the meta- 

 bolism. This is certainly the case with hydrocyanic acid, 

 and no doubt further investigation will show that it is the 

 same with other products similarly formed. 



Guignard (66, 67) has made similar researches to those 

 already described upon the plants of the natural orders 

 Cruciferae, Capparidaceae, Tropceolacese, Limnanthaceae, 

 Resedaceae and Papayaceae ; which all contain the ferment 

 myrosin, a body capable of decomposing more than one 

 glucoside. There are several of the latter compounds 

 found in this group of plants, the best known of which are 

 sinio-rine, anc j sinalbine. Siniorine is found in the black 

 mustard (Brassica nigra), and is often called myronate of 

 potassium. On decomposition it yields besides sugar a vola- 

 tile body, sulphocyanate of Allyl, and potassic hydrogen 

 sulphate. Sinalbine, as its name implies, is found in the 

 white mustard (Sinapis or Brassica alba). When decom- 

 posed the volatile constituent is found to be sulphocyanate 

 of orthoxybenzyl. Others, the composition of which is not 

 yet fully known, are those of the watercress {Nasturtium 

 officinale) which yields phenyl propionic nitrile, the common 

 cress {Lepidium sativum) affording the nitrile of alpha- 

 toluic or phenylacetic acid. Though the fate of these 

 complex volatile bodies has not been investigated, it is 



