THE FRUIT AND SEED-DISPERSAL 



299 



CYCLE OF LIFE. 



The germination of the seed, and the re-establishment of the 

 sporophyte as its result, completes the normal cycle of life of the 

 Flowering Plant. The leading incidents of that cycle may be re- 

 presented by a diagram, which will serve later as a means of ready com- 

 parison with types of vegetation lower in the scale (Fig. 244). It will 

 be found in them all that the leading events succeed one another in a 

 sequence that is uniform, however different the details may appear. 

 Two critical points in the cycle are marked by the fact that the 



VEG'-'PRO* 



MlCROSPORE. MECA5PORE. 



CONTENTS Of 

 POLLEN-GRAINTUBE 



FIG. 244. 



individual life is there presented in 'each case by a single cell. They 

 are the Spore and the Zygote : the former follows on reduction, and 

 is haploid ; the latter results from fertilisation, and is diploid. 

 Between these, and derived respectively from them, are two phases 

 of cellular amplification, so as to form a soma, or plant-body. 

 The one is the Sporophyte or rooted plant, which springs from the 

 Zygote, and is diploid ; the other is rudimentary in the Flowering 

 Plants, though it is more fully represented in lower forms. It is 

 initiated by the haploid spore, and is itself haploid. It consists here 

 of only a few cells contained on the one hand in the embryo-sac, on the 

 other in the pollen-grain and tube. It is called the Gametophyte. 

 These two phases together constitute the alternating Cycle of Life 

 of the Flowering Plant, which thus shows an Alternation of 

 Generations. 



