Reproduction in Multicellular Plants - 207 



Fig. 12-5. Hundreds of fern gametophytes (prothallia) 

 growing on the moist wall of a small flower pot. This 

 photo shows the approximate actual size of the gameto- 

 phytes. (Copyright, General Biological Supply House, 

 Inc.) 



the sporophyte generation are diploid. In the 

 sporangia, however, the spores arise by 

 meiosis from spore mother cells, and each 

 haploid spore represents the beginning of the 

 gametophyte generation. Each spore pro- 

 duces all the cells of the gametophyte by 

 mitosis, and consequently all the cells of the 

 gametophyte remain haploid. Higher plants, 

 therefore, differ from higher animals in that 

 the gametes of the plant arise by mitosis 

 from the haploid cells of the gametophyte; 

 or to state the matter differently, plants have 

 developed a haploid generation that inter- 

 venes between meiosis and fertilization (Fig. 

 12-7). 



TYPES OF LIFE CYCLES IN VARIOUS 

 PLANTS 



The main branches, or phyla, of the plant 

 kingdom embrace a multitude of species; but 

 all members of any one phylum have in- 

 herited a similar pattern of structure and 

 function. Consequently it is possible to de- 

 scribe the life cycles of the different groups 

 in fairly general terms. 



RHIZOIOS 

 FOOT. 



ROOT 



STEM 

 FIRST LEAF 



UPPER SURFACE 



NECK OF ARCHEGONIUM 

 APICAL NOTCH 

 VENTER 



Fig. 12-6. Note how the embryo sporophyte originates from a fertilized egg (zygote) 

 in the archegonium of the parent gametophyte (prothallium). The young sporophyte uses 

 its foot for the absorption of organic nutrients from the parent— until its own root, stem, 

 and leaf systems have developed adequately. 



