106 PRIMITIVE FORMS OF LIFE 



at first been possible only in very humid or even marshy soil, 

 and which was transplanted to dry soil, the male catkins, 

 always present in Gymnosperms and the Amentaceae, have dis- 

 appeared from the latter, and the female catkins alone have 

 persisted and become hermaphrodite. From this fact alone, 

 the explanation of the habitual form of flowers becomes easy. 

 We may assume that the hasty and precipitate formation of 

 fertile leaves, stamens, and carpels in a floral bud which is 

 undergoing especially rapid development has caused the dis- 

 appearance of the rudimentary infertile leaves which generally 

 accompany them, and which in the cone of the Gymnosperms 

 are mingled with them in various ways. These leaves, as a matter 

 of fact, are represented by little scales in the Plane-tree catkin, 

 and by little knobs in the case of the Willows and the Poplars ; 

 they are completely absent in the female catkins of the Birch, 

 in all those of the Myricinacese, and in the Oaks, Hazels, 

 Chestnuts, and the ordinary and white Beeches. Here the 

 catkin is protected by other infertile leaves called bracts, 

 grouped together by their bases and forming the cup for nuts 

 like the acorn (that of the hazel-nut surmounted by long leaf- 

 like appendages), the bur of the chestnut, the beech-mast, and 

 the envelope of the fruit of the horn-beam. In these plants, 

 almost all of them large trees or bushes, the flowers still possess 

 neither calyx nor corolla. Although they also demonstrate the 

 contingent character of the accessory parts of the flower, we need 

 not be concerned with those cases in which, as in many groups 

 of Monocotyledons, Juncaceae, Cyperaceae, Gramineae, Naia- 

 daceae,and Lemnaceae, the perianth, normally developed in other 

 plants, has become reduced and finally abortive. The instance 

 of the Arums is particularly interesting, because it shows 

 how the reduced perianths of flowers grouped in an ear can 

 be replaced by a huge bract capable of taking on the aspect of 

 the most brilliant perianth. 



Let us imagine a female catkin composed entirely of fertile 

 leaves, protected at its base by sterile bracts, which, under 

 unaccustomed conditions of nutrition, such as must have 

 frequently occurred when plants became more exclusively 

 terrestrial, is subjected to an accelerated development. The 

 first fertile leaves formed in the course of the elongation of 

 the catkin, those that occupy its base, will compete for their 

 nutrition with the catkin itself. As in the protandrous 



