SEEDS AND SEEDLINGS. 



209 



envelope grows up around the seed; an example of this is 

 found in the case of the red berries of the ' ' yew ' ' (taxus), the 

 red outer coat being an extra growth, called an aril. 



In the willow and the milkweed an aril is developed in the 

 form of a tu'ft of hairs. (In the willow it is an outgrowth of 

 the funicle, = stalk of the ovule, and is called a funicular aril ; 

 while in the milkweed it is an outgrowth of the micropyle, = 

 the open end of the ovule, and is called a micropylar aril. ) 



343. Increase in size during seed formation. — Accompany- 

 ing this extra growth of the different parts of the ovule in the 

 formation of the seed is an increase in the size, so that the seed 

 is often much greater in size than the ovule at the time of fer- 

 tilization. At the same time parts of the ovary, and in many 

 plants, the adherent parts of the floral envelopes, as in the apple; 

 or of the receptacle, as in the strawberry; or in the involucre, 

 as in the acorn ; are also stimulated to additional growth, and 

 assist in making the fruit. 



In the pine not only the ovular coat grows to form the outer 

 coat of the seed, the entire ' ' scale ' ' increases greatly in size, 

 and when the fruit is mature, a portion of this scale splits off 

 forming a " wing " to the seed (see fig. 169). 



344. Endosperm in the ripe seed. — In many seeds when they 

 are ripe there is still a large amount of the endosperm surround- 

 ing the embryo (albuminous seeds). 

 This is the case in the violet, as 

 shown in fig. 186. Other examples 

 of this kind are found in the butter- 

 cup family, the grasses, the lily, 

 palm, jack-in-the-pulpit, etc. When 

 the seed germinates this endosperm 

 is used as food by the embryo. _.. 



345. Endosperm absent in the Seed of violet, external view, and 



section. The section shows the em- 

 ripe Seed. In many Other plants bryo lying in the endosperm. 



all of the endosperm is consumed by the embryo during its 

 giqjrth in the formation of the seed. This is the case in the 



