108 PRIMITIVE FORMS OF LIFE 



These conditions are certainly fulfilled in a large number of 

 flowers, at any rate in certain of their parts, the andrcecium 

 or the gyncecium, of which the multiple elements are arranged 

 in spiral form like the scales of a pine-cone around its 

 axis. The Magnolias, the white Water-lilies {Nymphcea alba) , the 

 Camelias, and the Cactus also have such helicoidal flowers with 

 numerous elements, in which we can trace the development of 

 the sepals into petals (Camelia) or petals into stamens 

 (NymphcBa). In roses the leaves develop into sepals, and 

 although the latter are only five in number, they are gradually 

 modified. The number of petals is also five, all resembling 

 each other. The stamens, arranged in three whorls, are 

 always twenty in number, the carpels indeterminate, and 

 arranged spirally inside a cup hollowed out in the extremity 

 of the stem-axis. In the Strawberry, Raspberry, and Black- 

 berry, on the contrary, the axis protrudes, but the carpels have 

 the same arrangement. The calyx and the corolla are in whorl 

 formation, and the parts are all equal in the case of 

 the Buttercups, Anemones, Clematis, etc., but the stamens and 

 carpels are many in number. The latter become reduced in 

 number and fuse with one another, while the stamens remain 

 numerous, in the Poppy. Finally, all is regularized, tachy- 

 genesis shortens the axis which supports the various parts 

 of the flower ; parts of the same nature then arise 

 simultaneously, and their helicoidal arrangement disappears 

 completely ; sepals, petals, stamens, carpels, form so many 

 whorls of which the parts, equal in number, alternate from one 

 whorl to another. The flower is then said to be isomerous. The 

 last reduction of all affects the gyncecium, which may be formed 

 from carpels less in number than the corresponding parts of 

 the other whorls. 



Once the flower has been thus evolved, other causes can 

 modify it ; it can, for example, pass from the whorl form 

 to one symmetrical about one plane, as in the Papilionaceae ; 

 but, above all, under the influence of tachygenesis, the 

 parts of the same whorls may be formed so quickly that 

 they grow into one another, and the dialypetalous corolla 

 becomes gamopetalons. This fundamental division of the 

 Dicotyledons, which everyone recognizes, would thus appear to 

 be the result of such a process of tachygenesis. It is 

 tachygenesis, moreover, which in both these two series has 



