LECTURE X. 



example, for our knowledge of its chemistry is more com- 

 plete than is that of any other similar organ. 



Non-nitrogenous organic substance is conveyed to the 

 seed in the form of sugar, the nitrogenous in the form of 

 amides, and they are there deposited, the non-nitrogenous 

 substances in the form of starch or of oil, the nitrogenous in 

 the form of masses of proteid (consisting of peptones, globulins 

 and albuminates) known as aleurone-grains. It appears, there- 

 fore, that a formation of proteid takes place in seeds doubtless 

 from the sugar and the amides which are supplied to them. 

 The greater part of the sugar, however, reappears in the form 

 of starch or oil. It has been found in many cases that aspara- 

 gin and other amides are present in seeds in small quantity, 

 and occasionally nitrogenous glucosides are present, as, for 

 instance, amygdalin in the Bitter Almond, potassium myro- 

 nate in the Black Mustard. 



We may distinguish different kinds of seeds according to the form 

 and the place in which the reserve-materials are stored up. Thus there 

 are starchy seeds which contain much starch and more or less oil, and 

 oily seeds which contain oil and no starch : in the former the aleurone- 

 grains are small, in the latter they are large. Further, in some seeds the 

 reserve-materials are deposited in the cells of the seed itself, either 

 outside the embryo-sac (perispcrm\ or within it (endosperm], and in 

 some both perisperm and endosperm are present ; in others they are 

 deposited in the seed-leaves or cotyledons of the embryo which then 

 occupies the whole of the seed. Seeds of the former kind are said to be 

 albuminous^ those of the latter exalbuminous. 



We will defer, for the present, the consideration of the 

 structure and of the chemical composition of the starch-grains 

 and aleurone-grains. It need only be stated now that aleu- 

 rone-grains always contain a mass of mineral matter, the 

 globoid, and frequently a crystal of proteid, the crystalloid. 



These are the principal forms in which the reserve- 

 materials are stored up in seeds. Less frequently they 

 occur, in addition, in other forms ; thus in the seeds of the 

 Date and of Phytelephas carbohydrate is deposited in the 

 form of thickened cell-walls, that is, as cellulose, consti- 

 tuting, in the latter case, what is known as "vegetable 

 ivory"; again glucosides are occasionally present, substances 



