418 Nature and Causes of Variation in Plants. 



case, whicli the reader will readily develop. A wider 

 consideration shows the gradual shortening of the sexual 

 generation from the Mosses onwards through the Lycopods, 

 EquisetacecC, Ferns, Cycads, and Ooniferse, to the phanero- 

 gams, where it is represented by pollen grain and embryo- 

 sac alone. The comparative failure of the moss type seems 

 thus due to an inevitably unsuccessful attempt at vege- 

 tative life on the part of the reproductive generation. 



It is seen from cases such as the above-mentioned, that 

 the reproductive axis, organ, tissue, in every case tends to 

 become more and more shortened, depressed, or hollowed 

 in proportion to the vegetative. In wider terms, whenever 

 destructive changes in protoplasm predominate over con- 

 structive, the tendency is thus to produce a concave surface, 

 as seen, for example, in the hollows of nectaries, or in the 

 invagination of the blastosphere to form the gastrula 

 (see fig. D). 



This conception may be further developed, and shown 

 to apply alike to the construction of the general genealo- 

 gical tree, and, in particular, to the affinities of the 

 flowering plants, and even frequently to the interpretation 

 of the minute details of floral structure usually regarded 

 as the product of natural selection acting on " spontaneous " 

 local variations, nor need its application be restricted to the 

 vegetable kingdom only. 



The Botanico-GeograpMcal Exliihition at Copenhagen in 

 1885, instituted hy M. Carl Hansen, Professor of 

 Agriculture at the Royal Academy, Copenhagen. By 

 Andrew Taylor. 



When delivering a course of lectures on Botanical 

 Geography early in April 1885, it occurred to Professor 

 Hansen that his work needed more thorough and popular 

 illustration than that afforded by diagrams and tables 

 when exhibiting orographic distribution, or plant migra- 

 tion, caused by atmospheric or oceanic currents, as well 

 as the influence of man. The Professor accordingly in- 

 stituted a small exhibition of 2000 live plants in pots, 

 arranged so as to demonstrate to the eye the recognised 



