12 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 30 Ser. 



IV. The Flowers. 



The flowers of Naias represent the simplest form which 

 an angiospermous flower can assume, consisting simply of a 

 single carpel with but one ovule, or of a single stamen, which 

 in most species has but one pollen cavity. In origin and 

 in their earlier phases of development, ovule and stamen 

 present very marked similarity, and this is heightened by 

 the development about the stamen of structures correspond- 

 ing to the integument of the ovule, and of an envelope which 

 imitates very closely the carpellary covering of the ovule ; 

 this even extending to the formation of similar teeth at the 

 apex. The resemblance of both to the sporangia of certain 

 Pteridophytes, especially Azolla, where the macrosporan- 

 gium has a similar investment, is also noteworthy. 



As we have seen, the rudiment of the flower is formed 

 by the equal division of the primordium, which is formed 

 above the lower of each pair of leaves. At first these are 

 not distinguishable, but very soon one of them becomes 

 somewhat larger than the other (fig. 11, f), and this, which 

 is the young flower, soon develops about it a ring-shaped 

 wall — the carpel or its equivalent — and thus is readily dis- 

 tinguishable from the other protuberance, which is also 

 more pointed and becomes the apex of the lateral shoot. 

 It is thus plain that the origin of the ovule or anther, as the 

 case may be, is strictly terminal; i. e., that the flower and 

 the lateral branch are due to the dichotomy of a common 

 primordium. and therefore are of equal morphological value. 

 The male and female flowers are scarcely distinguishable at 

 first, as the envelope about each is entirely similar; but as a 

 rule the young ovule is somewhat more slender than the 

 anther. The question of the homologies of the envelopes 

 of the flowers will be better understood after considering 

 the development of the latter. 



I. The Male Flower. — Shortly after the separation 

 of the primordium into the rudiments of the lateral branch 

 and flower, the latter grows much more rapidly, and its real 

 nature becomes evident. It begins to broaden at the base 



