218 THE BOTANICAL MAGAZINE, rVo i. xxiv. No. 2S4. 



the occasion of the climatic and other external changes, and the 

 consequent fate of extinction. Thus the extinction of individual 

 species is ascribed to the change of environments. 



4 Struggle ' with other vegations, not to speak here of the 

 parasitic or other injurious organisms, with respect to the oc- 

 cupation of habitat, reach of light etc., need not be specially 

 mentioned as among the causes. But this ' struggle ' will cer- 

 tainly fail to explain in many cases the dying- out of the species. 



The general condition to be accounted for seems after all to 

 be the change of climate, to which those individual species now 

 only known as fossils, found , unable to adapt themselves. As 

 the change of climate and environments in general would have 

 been a great factor of evolution in the history of organisms, (1 

 it would have been likewise the chief factor worked upon to the 

 destruction of species. 



In closing I may attempt to get into a cytological line of 

 inquiries about the cause or circumstances which may lead to dy- 

 ing-out of a group or a certain line of desscent. As we recognise 

 the external and also the internal structural differences among 

 the plants of different groups or descent, with regard to the 

 protoplast in general as well as the cell-wall, quite reasonably 

 we may expect to find the differences of chromosomes of cell 

 nucleus in plants of different types or descent, in the num- 

 ber, shape, arrangement, behavior etc, and the visible structure 

 of individual chromosomes. The numbers of chromosomes are 

 now known in a large number of plants, although the exact 

 shapes of individual chromiozomes are known only in a com- 

 paratively small number of cases. 



It was highly desirable in this line of thought, to know 

 if we could find any difference regarding the chromosomes 

 between the plants of archaic type now represented more or 

 less as a kind of relic plants and the plants of youngest type ; 

 thus to see on one hand, if the visible features of chromosomes 



(1) If the earth were still deeply covered by water, and no land appeared yet, 

 it would be highly probable that we had, as far as plants is concerned, nothing but 

 Algae and other Thallophyta. 



