386 



GENERAL MORPHOLOGY OF PLANTS 



Ripened ovule. ( 



by the forming embryo, and is stored in the cotyledons, as in the 

 bean, pea, oak (exalbuminous seeds), and the remnant of the 

 endosperm forms a thin papery membrane around the embry, . 

 All of these changes take place within the ovule while it is still at- 

 tached to the ovary and nourished by the sporophyte. The seed 

 at maturity then consists of the embryo, surrounded by the endo- 

 sperm or its remnants, and the seed coats which are formed from 

 the coats, or integuments, of the ovule. In some seeds there is 

 in addition the perisperm (see paragraph 548) . 



551. Synopsis of the seed. The following table will show 

 those parts composing the seed. 



Aril, rarely present.* 



Ovular coats (one or two usually present), 



the testa. 



Funicle (stalk of ovule), raphe (portion of 

 funicle when bent on to the side of ovule), 

 micropyle, hilum (scar where seed was 

 attached to ovary). 



Remnant of the nucellus (central part of 

 ovule); sometimes nucellus remains as 

 Perisperm in some albuminous seeds. 

 Endosperm, present in albuminous seeds. 



Embryo within surrounded by endosperm when this is present, 

 or by the remnant of nucellus, and by the ovular coats 

 which make the testa In many seeds (example, bean) 

 , the endosperm is transferred to the cotyledons which 

 become fleshy (exalbuminous seeds). 



COMPARATIVE REVIEW OF THE ANGIOSPERMS. 



552. Origin of the Angiosperms. Botanists are not agreed 

 as to the origin of the Angiosperms, nor as to whether the mono- 

 cotyledons or dicotyledons were the lowest group. Some have 

 suggested that the Angiosperms were derived from 'a Gymno- 

 sperm-like ancestor similar to Ginkgo, while others believe they 

 were perhaps derived from early plants similar to some of the 



* The aril is present in ginkgo and the yew, as a collar at the base of the 

 ovule which in the yew grows to form the red fleshy covering of the berry. 

 In the milkweed and willow there is a hairy aril. 



The seed. 





