EARLY SPRING 47 



The seed is a jjlant in embryo. It consists of a young root, a 

 bud, and one or two seed-leaves or cotyledons. Some seeds con- 

 tain nothing but the parts just named, and when this is the case the 

 cotyledons contain a reserve of food material sufficient to maintain 

 the developing plant until the root is enabled to absorb sufficient 

 nutriment from the soil, and the fu'st foliage leaves are so far 

 advanced that they can absorb carbonic acid gas from the ak, and 

 build up with the aid of this gas, together with the food obtained 

 from the soil, the compounds required by the growing plant. 



Other seeds contain, in addition to the embryo, a reserve of 

 nutrient material quite distinct from it ; and in such instances the 

 cotyledons have the power of taking up this reserve, changing it to a 

 condition suitable to the requirements of the plant, and then dis- 

 tributing it to the growing parts. 



In some seedHngs the cotyledons will remain for some time 

 within, or partially within the seed, in order that they may continue 

 the absorption of this reserve ; and while this process is going on the 

 seed may remain below the smface of the soil, or it may be Ufted 

 into the air by the upward growth of the cotyledons themselves. 



In cases where the cotyledons contain the food reserve for the 

 seedUng they sometimes remain under the soil, but in many instances 

 they are pushed into the air by the upward growth of that portion 

 of the plant axis immediately below them. In either case they 

 decay as soon as their work is accompHshed. This often happens 

 as soon as they have delivered up to the seedling their reserve of 

 food, but frequently the cotyledons which ascend into the air 

 expand, becoming really leaflike in general appearance, assuming 

 a green colom- through the development of chlorophyll (the green 

 colouring matter of plants), and then perform all the functions of 

 the ordinary foliage leaves of the plant. Such cotyledons often 

 continue to exist long after the first fohage leaves have appeared 

 from the bud, for, although the original food reserve has been ex- 

 hausted, they are now in a position to manufacture, under the 

 combined influence of the sun's warmth and Hght, compounds 

 essential for their own growth as well as that of the other parts of 

 the seedling. These cotyledons, however, are never of the same 

 form as the true fohage leaves. 



The student should obtain a variety of seeds or seedUngs of 

 our wild plants and forest trees in order to study these interesting 

 early stages. Such employment will prove very valuable at a 

 season when there is but httle call for outdoor work. 



