Nov. 1894.] BOTANICAL SOCIETY OF EDINBURGH. 283 



development of the first spore-mother-cells of the resulting 

 sporophyte. And in most of the vascular plants, where 

 'successive crops of fertile spores may be formed, the period 

 may vary for different and successive parts of the same 

 individual plant. 



Considerations such as those we have now discussed 

 may be expected to modify our view of the meaning and 

 origin of antithetic alternation. The neutral generation is 

 now very generally regarded as a result of elaboration of 

 the zygote, and thus it is a phase intercalated during 

 descent into the life-cycle. I have suggested, elsewhere, as 

 the chief cause of its origin the migration of aquatic forms 

 to the land, in which case sexuality by motile spermato- 

 zoids would be checked, and only take place at intervals, 

 while the increase in number of individuals having to be 

 attained by some other method, spore-formation in increas- 

 ing numbers would come into effect. In view of the facts 

 and conclusions brought forward by Strasburger, I see 

 reason to modify, but not to abandon, that opinion. The 

 migration to a land habit has probably been a dominant 

 influence in leading to an increased output of spores, as 

 illustrated by the ascending series of the Archegoniatae ; but 

 it may be a question whether it was the prime cause of the 

 sub-division of the zygote. The fact that such sub- 

 division is found in Alg?e of the Confervoid series, and the 

 further facts connected with the germination of zygotes of 

 the Conjugatse, etc., appear to suggest that the initial 

 impulse to sub-division of the zygote is to be sought in 

 connection with the steps of sexual coalescence, and sub- 

 sequent reduction of the doubled number of chromosomes. 

 But until the facts are better known in such plants as 

 (Edogonium, Sphceroplca, and Colcochccte, it is impossible to 

 progress beyond the area of surmise. 



The above remarks are such as the stimulating paper of 

 Professor Strasburger has impelled me to put before you. 

 There can be no doubt that the detailed work of the last 

 few years, culminating in the address at Oxford, will give 

 a new impulse to the study of plants showing antithetic 

 alternation. It remains for the investigators of to-day to 

 carry on the work of Hofmeister. We may reasonably 

 hope that their efforts may end in raising the whole 



