DEVELOPMENT. 75 



have this perisperm surrounding their embryo. A simi- 

 lar substance is found in the seeds of mangel ; the seeds 

 of turnips, peas, beans, and clover, on the other hand, 

 are destitute of it. An embryo plant consists of a radi- 

 cle, or rudimentary root, surmounted by a caulicle, 

 which is often so short as to be imperceptible to the 

 naked eye, but from which spring the seed-leaves, or 

 cotyledons one only in the case of all the cereals and 

 grasses, two in the case of the other crops of the farm. 

 In the case of the wheat grain, where the perisperm is 

 abundant, the cotyledon is small and thin ; but in the 

 pea or bean, where the perisperm is absent, the cotyle- 

 dons are very thick and fleshy. The difference depends 

 upon the presence, in the one case, of large quantities of 

 reserve-materials in the embryo itself, while in the case 

 of the wheat the reserve-materials are stored up in the 

 perisperm. 



The seed, then, in addition to the young plant, con- 

 tains in the tissues of the embryo plant itself, or in the 

 perisperm surrounding it, reserve -materials destined to 

 supply the young plant with food during its growth and 

 development. 



Reserve-materials: their Transport. Under the 



head of nutrition, mention has been made of the sub- 

 stances formed in plants through various agencies. Some 

 of these are used up at once during growth, while others 

 are reserved for future use, having usually undergone 

 some change in constitution to fit them for their purpose. 

 Speaking broadly, these reserves are either starchy, oily, 

 or albuminoid (nitrogenous) in their character. The 

 starchy or oily ingredients are the direct products of the 

 action carried on under the influence of sun light in the 

 cells containing chlorophyll. Starch cannot be formed 

 in cells containing no chlorophyll, nor, for a continuance, 

 in chlorophyll-containing cells, unless they are exposed 



