102 PRIMITIVE FORMS OF LIFE 



rolled up in a cone-shaped receptacle so as to conceal the 

 ovules, and it is thus their name of Angiosperm arises. At the 

 same time the prothallus is still further reduced in the ovule ; 

 the cell which gives rise to it, and which is called the embryo 

 sac, increases in size ; the nucleus generally undergoes only 

 three successive subdivisions, which give rise to eight nuclei ; 

 two of these nuclei fuse into a single one occupying the centre 

 of the embryo sac, three others are arranged at its base, 

 and the last three at the top, where they form the basis of an 

 equal number of cells. Of these three cells one only is trans- 

 formed into an oosphere ; the others remain sterile, and all 

 traces of the archegonia are lost. The microspores or pollen 

 grains do not themselves contain more than two nuclei, one of 

 which is subdivided to form two others, the last relics of the 

 antherozoids. 



Anyone who has followed this evolution must realize that it 

 is the characters produced by tachygenesis which distinguish 

 the three large groups of Rhizophytes or plants possessed of 

 roots and vessels : the Cryptogams, the Gymnosperms, and 

 the Angiosperms. It is evident that these three classes 

 successively developed their characters in the order we have 

 just indicated, and could have appeared on our earth in no 

 other order. Tachygenesis, however, goes still further in the 

 Angiosperms. The reproductive leaves of the same sex are all 

 grouped together in the Gymnosperms, and arranged in a 

 tight spiral, forming what we know as a cone ; there are both 

 female and male cones, generally found on the same tree ; 

 hence the conifers are said to be monoecious. The Angio- 

 sperms, like the Gymnosperms from which they are directly 

 derived, ought to have " flowers " reduced to the essential 

 parts ; those of the same sex ought to be grouped together, 

 either on the same tree or on two separate trees. This actually 

 occurs in the large family of the Amentacese, which group their 

 flowers in unisexual catkins, or sometimes reduce them, as in 

 the case of certain willows, to two stamens protected by a 

 simple scale. 



How was it possible for catkins to evolve into true flowers, as 

 botanists understand the term ? Flowers of the highest type 

 consist of four whorls. Two are of sterile leaves : these are the 

 calyx, whose leaves generally remain green, and the corolla, 

 whose leaves are usually coloured. The two other whorls are 



