346 CHARACTERS OP NATURAL SYSTEM. 



tingtrishing orders. A peculiar enlargement of the receptacle, 

 which sometimes expands between the bases of the carpels so as 

 to separate them more or less completely (. 470), as in the 

 Strawberry, is often very characteristic of particular orders. 

 The ripened ovary or fruit exhibits numerous and remarkable 

 differences in its form, substance, and mode of dehiscence (or its 

 manner of bursting when ripe); but these do not usually receive 

 much attention from Botanists ; since although there are a few 

 orders which are characterized by a particular kind of fruit, most 

 others present numerous varieties among their different genera. 



500. Many valuable characters are drawn from the seed, 

 both in its early and mature conditions. The number of ovules, 

 that is to say, whether they are definite or indefinite, is 

 frequently an important difference ; still in some orders, there 

 are genera nearly allied, in one of which the number is definite, 

 whilst it is indefinite in the other. The position of the ovules is 

 more essential than their number; the chief distinctions are 

 between those which, rising upright from the base of the cavity, 

 are termed erect ; and those which, hanging from its top, are 

 called pendulous. Between these two conditions, however, there 

 are other intermediate ones. Such a difference in the position of 

 the ovules often serves to mark a distinct line of separation 

 between the plants of two groups that are otherwise nearly allied. 

 In the perfect seed, the number of cotyledons is a character of 

 primary importance, for distinguishing the two great classes of 

 Phanerogamia, as already several times stated. Even this, how- 

 ever, is subject to occasional exceptions; for there are Endogenous 

 Plants with two cotyledons, and some Exogens with only one, 

 or even none ; whilst again, some Exogens have several. As a 

 means of distinguishing orders, the presence or absence of a 

 separate albumen (. 439) is a character of great value, especially 

 when the embryo bears a very small proportion to it in amount, 

 as in the orders we shall first have to consider. Where, however, 

 the embryo and albumen are nearly equal in size, the character 

 is of less importance ; so that it is not uncommon to meet, in the 

 same order, with some genera, of which the embryo alone fills 

 the seed, and with others in which a part is occupied by albumen ; 



