236 LIFE HISTORY OF A FERN. 



the parts of the perfect plant ; and the production of roots, stem, 

 leaves, flowers, rei)roductive organs, and seed like to that from 

 which it sprung, is but a continuation of growth commenced in 

 the germination of the initial seed. There is thus from seed to 

 seed the perfect cycle of a life-history in one generation. 



The genesis of a spore is, however, essentially different. Here, 

 in the cycle of its life-history, we find two generations, sexual and 

 non-sexual in alternation, before we return to the point from which 

 we started with the spore. Moreover, the character of a spore is 

 quite distinct from that of a seed, inasmuch as it possesses neither 

 albumen nor embryo, and in its constitution approaches more 

 nearly to the pollen-grain, although widely differing from it in its 

 functions. 



The spore is an isolated cell, consisting of three parts. First, 

 an outer skin, somewhat irregular in its form and brittle, but des- 

 titute of the pores found in the extine of the pollen-grain. 

 Secondly, an inner integument exceedingly thin and elastic, which 

 encloses a fluid mass of protoplasm. Under favourable conditions 

 of warmth and moisture, germination commences by the outer 

 skin being ruptured and the inner skin becoming extruded, while 

 a vegetative process is set up in the contained protoplasm, minute 

 granules of chlorophyll are developed, and the young cell becomes 

 self-supporting, being capable of assimilation. Sub-division into 

 two cells is effected by the formation of a transverse septum. The 

 outer cell is again sub-divided, and there are now three cells placed 

 end to end, and still retained in contact with the ruptured spore. 

 The third cell is similarly divided, and now, in addition to the 

 transverse septum, another wall is formed at right angles to the 

 former, separating the cell into four parts. The growth thus pro- 

 ceeds by repeated transverse and longitudinal bipartition, until a 

 somewhat heart-shaped, flattened expansion of cells is the ultimate 

 structural result. This is called the prothallium. 



On the under side of the prothallium, by the unequal growth 

 of the cell-walls, long, unicellular root-hairs are formed by which 

 water and soluble earth-salts are absorbed. A further development 

 now ensues, and the reproductive organs are formed upon the 

 same side — viz., the antheridia, or male organs, on the lower part^ 

 and the archegonia, or female organs, on the upper part of the 

 prothallium. 



