588 BOTANY OF THE LIVING PLANT 



In the latter the association is ultimately followed by nuclear fusion, 

 which thus, though deferred, takes its place in the cycle. The fact that 

 similar nuclear fusions precede the formation of ascospores (p. 419) and of 

 basidiospores (p. 432) suggests that such methods are probably wide-spread 

 among Fungi. The nuclei involved in such cases spring not from any widely 

 distinct sources, but from cells closely related in position and in origin. It is 

 remarkable that these and other irregularities in the sexual cycle are found 

 commonly among Plants represented by very numerous closely related forms. 

 If their numerous species and varieties have resulted from mutation, then it 

 would appear that excessive mutation may have had some influence in 

 producing those irregularities. In organisms which mutate freely, the 

 Mendelian sifting out, and preservation of each heritable mutation, would be 

 a less vital matter than it is in more stable forms. This may in some degree 

 account for such deviations from the normal sexual reproduction as have just 

 been described. 



