THE STOEAGE OF EESEEVE MATEEIALS 253 



tained in fleshy roots and stems. Many plants belonging 

 to the Cruciferce and several allied orders are particularly 

 rich in reserve materials belonging to this group. Sini- 

 grin, or myronate of potash, is the principal glucoside 

 which they contain. It splits up into sulphocyanate of 

 allyl, grape-sugar, and hydrogen-potassium-sulphate. 



The nutritive value of these bodies is partly due to the 

 sugar which they yield on decomposition. The evidence 

 that the other products can minister to nutrition is not 

 very complete, though it seems satisfactory in certain 

 cases. 



Fats or oils are frequently stored as reserve food -stuffs 

 in different plants. The distribution of this material is 

 very varied, though, as in so many other cases, the seed is 

 the most general place of deposition. Many seeds, that 

 for instance of the castor-oil plant, contain as much as 60 

 per cent, of their dry weight of oil, which is non-volatile. 

 Others contain as little as 2 per cent., and between these 

 limits very varying amounts may be found. When the oil 

 is in great preponderance, it is usual for no other form of 

 carbonaceous reserve to be present ; in cases where but 

 little oil occurs starch is usually found as well, as in so 

 many of the Leguminosce. The Cruciferce as a group 

 often contain oil in fairly large quantity. As a rule nitro- 

 genous reserves in the shape of aleurone grains accompany 

 the oil. 



In other places than seeds large deposits of oil often 

 occur, though their purpose is not so obvious. We have 

 them in large amount in the pericarps of certain fruits, 

 such as the olive ; in the petals of many flowers, e.g. 

 Funkia and Ornithogalum ; in the leaves of some of the 

 Agaves, the roots of Oncidium, &c. They can hardly be 

 regarded in some cases as truly reserve materials, being 

 perhaps more strictly connected with the mechanisms of 

 dispersion. 



The mode of deposition of oil or fat is not at all well 

 known. It is generally found saturating the protoplasm of 



