EVOLUTION 965 



arranged round the axis, whose internodes are suppressed. The first 

 advance is to a definite number of sepals, petals, stamens, and 

 carpels in the arrangement called hypogynous. A carrying on of the 

 outer parts of the axis gives the perigynous position to the stamens, 

 and the final form is the epigynous, where stamens, petals, and 

 sepals are all carried past the ovary, the carpels occupying the 

 inside of a pit instead of the outside of a cone (see Fig. 162). 



Both these cases are clearly explicable by reference to the familiar 

 antagonism between reproduction and vegetative growth, which 

 may be analysed back to its basis in the constructive and destructive 

 metabolism of protoplasm. We may view in the same light the 

 concave form of the spore-bearing surfaces in many Fungi and 

 Algae — for instance, Peziza or Fucus — and even the emarginate 

 form of the fern prothallus, where the sexual organs appear. 



Note also that the shortening and reduction in the inflorescence 

 of the Coniferse from fir-cone to yew-"berry" is parallel to that of 

 the phanerogams. The reduction of indefinite to the various forms 

 of definite inflorescence is another change in the economy of the 

 phanerogam. Similar to this is the reduction and even loss of bracts, 

 and usually of petioles and stipules in the sepals. The complete or 

 partial loss of the calyx and petals is usually considered degenerate ; 

 but from the present economy point of view, it seems a more com- 

 plete specialisation for reproduction. In getting rid of coloured and 

 merely attractive organs, and assuming wind fertilisation, the 

 vegetative system is still further reduced. 



The lessening in the number of stamens, carpels, and ovules in 

 all the more evolved orders of plants is a parallel case, which the 

 reader will readily develop. A wider consideration shows the gradual 

 shortening of the sexual generation from the Mosses onwards 

 through the Lycopods, Equisetaceae, Ferns, Cycads, and Coniferae, 

 to the phanerogams, where it is represented by pollen grain and 

 embryo sac alone. The comparative failure of the moss type seems 

 thus due to an inevitably unsuccessful attempt at vegetative life 

 on the part of the reproductive generation. 



It is seen from cases such as the above-mentioned that the 

 reproductive axis, organ, tissue, in every case tends to become 

 more and more shortened, depressed, or hollowed in proportion to 

 the vegetative. In wider terms, whenever disruptive changes in the 

 protoplasm predominate over constructive, the tendency is to 

 produce a concave surface, as seen, for example, in the hollows of 

 nectaries, or in the invagination of the blastosphere to form the 

 gastrula. 



This conception may be further developed, and shown to apply 

 alike to the construction of the general genealogical tree, and, in 

 particular, to the affinities of the flowering plants, and even fre- 

 quently to the interpretation of the minute details of floral structure 



