318 



BOTANY. 



B. POLYGYNCEOIAL FRUITS. 



formed by the gynoecia of several flowers. 



1. A spike witli fleshy bracts and perianths — e.g., 



Mulberry , SOROSIS 



3. A spike with dry bracts and perianths — e.g., 



Birch Strobile. 



3. A concave or hollow, fleshy receptacle, enclosing 



many dry gynoecia — e.g.. Fig ..Stconus. 



§ 7. The Seed. 



The seed is the ripened ovule, and as the ovule consists of a tody, 

 surrounded by one or two coats or integuments, we may look for a like 

 structure in the seed. However, the modifi- 

 cations which most seeds undergo render 

 necessary some additional terms. Thus the 

 outer integument is generally so thickened and 

 hardened that it is commonly called the testa.' 

 The inner is sometimes called the tegmen. In 

 some seeds the outer coat becomes fleshy, in 

 which case they are baccate (beriy-like) ; in 

 others the outer part of the testa is fleshy and 

 FiG.220.— Comoseseed tlie inner hardened, so that the seed is drupa- 

 of Milkweed. ceous (drupe-like). Occasionally an additional 



coat forms around the ovule after fertilization ; it differs somewhat in 

 nature indifferent plants, but all are commonly included under the 

 name aril — e.g., in May-apple. 



The testa may be prolonged into one or more flat extensions ; such 

 a seed is winged — e.g., Catalpa. Its epidermal cells may be pro- 

 longed into trichomes, forming the comose seed — e.g., milkweed 

 (Fig. 230). 



Fig. 221.— Embryos dissected out from seeds: 1, showing at o the "radicle;" 

 b, b, the first leaves (cotyledons); c, the third and fourth leaves (.plumule), 

 a, a straight embryo. 3, embryo folded upon itself (incumbent) , 



