148 Report S.A.A. Advanckmknt of Science. 



sides of tlie Lsthiuus of Panama. These have been separated since the 

 late Miocene or earlj' Pliocene, and can in manj' cases hardlj' be dis- 

 tinguished as varieties. The other is again taken from mj^ own subject. 

 Cleuient Read and Eleanor M. Read in a recent number of tlie Journal 

 of the Linngean Society {Botany, Januarj' 11th, 1908) published a 

 paper on the pre-glacial flora of Britain, and showed that there are 147 

 species of llowering plants, which, as shown by the remains of their 

 seeds or hard parts of the fruit, have persisted from pre-glacial times 

 to the present time. There does not seem to be the slightest doubt 

 about the trustworthiness of the results of these two workers. If 

 their results are accepted, then we may safelj'- conclude that a good 

 many more species have persisted through such a long period in such 

 a maimer as to show the same fine details by which seeds of allied 

 plants are distinguished. Of course, in any case, the plants identified 

 are onl}' those the remains of which are likelj' to be preserved in 

 estuaries, and those whose seeds are suitable for preservation in the 

 fossil state. This investigation throws sidelights on a number of 

 important (|uestions, and proves that many species have persisted 

 unaltered in Britain from pre-glacial times to the present day, and it 

 makes the conclusion justifiable that the majority of British plants 

 have done the same. 



The earlier botanists and zoologists were rather inclined to tr}^ to 

 make too much of the constancy of species, and looked upon variations 

 as a nuisance, as the3' interfered with their cast-iron rules of classifica- 

 tions. But even at an earl}'^ date after Darwin had tried to build up 

 his theor}' of descent on the basis of natural selection, and when many 

 looked upon species as mere shifting phantoms, some of our deepest 

 thinkers recognised that each species represents a definite entity, and 

 the problem how such entities could change into entities of a different 

 nature received a much deeper meaning. Thus Niigeli formed his con- 

 ception of the idioplasm and Weismann of the germ plasm. It is not 

 ni}- |)urpose to trace the historj^ of these conceptions and the theoreti- 

 cal conclusions developed from them. I will only brieflj'^ indicate 

 how, on the one hand, they led to the recognition of definite bearers 

 of specific ciiaracters, and how even there are strong signs that the 

 chemical constitution of the protoplasm is at the back of the con- 

 stancy of species, and that species change if this chemical constitution 

 is altered. I must, however, insist that we must use the word "con- 

 stancy ' in a restricted nieaning. The fact that a species is constant 

 does not exclude its exhibiting a wide range in fiuctuations, or, as tliey 

 are usually' called, variations. 



It was early recognised that the lasting characters of species are 

 located in the nuclei of the germ cells. The study of the mitotic 

 divisions of nuclei has contributed largely to clear our ideas on this 

 point, and when tiie reduction-.division in the sexual cells was dis- 

 covered, it became likely that the chromosomes weie actually the 



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