EVOLUTION OF ANGIOSPERMS THROUGH APOSPORY 165 



the apex downward. The terminal portions of the leaves and 

 inflorescences may be pushed out as finished products while 

 their basal tissues are still in a rudimentary and delicately pro- 

 toplasmic condition. 



The development of a series of capsules or cotyledon-indi- 

 viduals by apical budding or plumule-formation is certainly no 

 more remarkable than that new moss-plants should arise from 

 cells of the stem of a moss-capsule, or even from the lid. Nor is 

 it an any more improbable phenomenon than the development of 

 adventitious buds as a result of injuries to parts which normally 

 do not produce buds at all, as for example, in a piece of cotyle- 

 don of Plantago or in the embryo of Sechiiim^ which produces 

 new roots and new plumules if the originals fail of their pur- 

 pose. 



APOSPORY WITH DEFERRED MITAPSIS. 



The final step in the present suggestion of a course of evolu- 

 tion toward angiospermy is that the primitive cotyledon-like 

 plant becomes aposporous, so that it can produce prothalli 

 instead of spores, the fusion and reduction of the number of 

 the chromosomes (mitapsis) being deferred until the egg-cells 

 are to be formed. Apospory, with the retention of the double 

 number of chromosomes has been ascertained to exist in ferns 

 of the genus JVepht'oditun. 



"The prothalli of the two apogamous varieties, Ncfhrodium 

 pseudo-mas Rich. var. polydactyla Wills, and Nefhr odium 

 ■psciido-mas Rich. var. cristata afosfo7-a Druery, exhibit two 

 striking differences. Whereas in the former nearly all the pro- 

 thalli, except very young ones, have a strand of vascular tissue 

 extending throughout the greater part of their length, in the 

 latter only two cases of feebly-developed tracheides have been 

 seen. Again, in JVcpkrodittm pseudo-mas var. polydactyla^ mi- 

 grating nuclei, some of which have been seen to fuse, are a 

 characteristic feature. Out of a large number of prothalli it 

 was found that about 73 per cent, of the 3^oung ones exhibit 

 phases of nuclei passing from one cell to another. As this fern 

 produces fertile spores, it is almost certain (it is hoped shortly 

 to settle this point) that there is a true reduction during the 

 division of the spore mother cells, the doubled number charac- 



