GERMINATION OF THE SPORES 



217 



Other, where they fuse and form at each pole a resting spore 

 nucleus. 



Let us now recapitulate these processes in somewhat briefer 

 terms, (a) The chromosomes that appear in the division of 

 the nucleus of the spore grandmother cell are closely associated 

 in pairs, (b) A pair is not formed by the longitudinal division 

 of a preexisting chromosome, but by the approximation of two 

 parts of the nuclear thread before its transverse segregation into 

 chromosomes, (c) The members of a pair now separate and 

 are drawn to opposite poles, (d) Traveling poleward each 

 chromosome shows that it has become split longitudinally, (e) 

 At the poles the split chromosomes form a nuclear reticulum 

 which becomes enclosed in a nuclear membrane, thus forming 



Fig. 124. — A, B, C, D, Successive stages of growth of prothallium from the spore in 

 Osmunda cinnamomea ; E, growth of fern plant from fertilized egg within the prothallium 

 of Osmunda Claytoniana. (After Campbell.) 



the resting nucleus of the spore mother cell, (f) When this 

 mother-cell nucleus begins division the split chromosomes appear 

 again as such, and in the anaphase their halves are sundered 

 and removed to opposite poles where the spores are now formed, 

 two for each mother cell, four for each grandmother cell. 



Germination of the Spores. — When the ripe spores of 

 Osmunda have fallen in a favorable situation they immediately 

 germinate (Fig. 124, A, B, C, D), and produce a small, pros- 

 trate, chloroplast-bearing body called the prothallium, D, which 



