Structure of Seeds 5 



may originate from two different parts of the ovule or unripe 

 seed, and hence is known either as endosperm or perisperm. 

 This will be more apparent when we have dealt with the growth 

 of the ovule. 



The term albumen is rather a misleading one, as it might 

 lead the student to imagine that the substance contained within 

 the seed is identical in chemical composition with animal albu- 

 men, such as is found in the white of an egg, whereas it differs 

 in its characteristics in various plants. In cereals it is meafy 

 or farinaceous ; in the Barberry and Heart's -ease it vs, fleshy ; in 

 the Poppy and Cocoanut it is oify ; in the Mallow, mucilaginous; 

 in the Vegetable Ivory and Coffee, horny. 



Seeds containing albumen are spoken of as albuminous, 

 whilst those destitute of it are exalbuminous. 



We may tabulate the structure of the most perfect seed as 

 follows : — 



f Testa f Albumen 



Spermoderm < t. Nucleus < f Radicle 



\Tegmen [Embryo i Plumule 



L Cotyledons 



There is another point in which seeds differ. On examin- 

 ing a grain of Wheat, or of an allied cereal, we find that there 

 is only one cotyledon present, instead of, as in the case of the 

 Bean, two. Several plants resemble the Bean ■ in having two 

 cotyledons present in their embryos ; whilst others, like Oats, 

 have but one. This causes the division of the sub-kingdom of 

 Flowering Plants into two groups : Dicotyledons include 

 those Phanerogams with two (or in some Conifers more) 

 cotyledons ; whilst Monocotyledons are those with only one. 

 As we proceed further we shall find that there are other differ- 

 ences between these tvro great classes. 



