20 BOTANY 



The germination of the seed is the waking of these 

 same organs to life and further growth. In the growth 

 and development which follows the germination of the 

 seedling there are many features of considerable morpho- 

 logical interest. The young plant often tends to repeat 

 in its own life history some of the stages through which 

 its species passed as a whole in its evolution. Thus 

 we find in the development of plants with divided, 

 complex leaves that the first three or four leaves of the 

 seedling are simpler, and it is only as it grows that it 

 attains the elaborate adult foliage. Plants, too, which 

 have specialised stems or elaborate structures to re- 

 place ordinary foliage, will generally have a much 

 simpler and more normal structure when they are very 

 young. The study of seedlings is, therefore, a very 

 useful factor in attempting to elucidate some of the 

 morphological problems. 



So far we have considered only the body of the higher 

 plants, in which, though there is infinite variety of detail, 

 there is a uniformity of plan throughout. Among many 

 of the lower plants we find the vegetative body com- 

 posed of the same set of organs root, stem, and leaf 

 as in the case of the higher plants. Further comparison 

 is rendered more difficult by the fact that the alterna- 

 tion of generations, common to nearly all plants, is 

 in them expressed in terms of two distinct individuals, 

 and a small green plant (known as the Prothallus) 

 bears the sexual cells of the large, leafy fern. The 

 prothallial plant is produced from the spores of a simple 

 kind which are often borne, not on flowers, but on the 

 ordinary foliage of the vegetative plant. All our 

 common ferns have this character, and the brown 

 marks on the leaves are clusters of small sporangia, 

 while the little prothallial plant they produce is gener- 



