96 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



these have the same effect as drought. Coupled with this is the continuous 

 illumination, which tends to arrest the stem-growth. 



A juniper stem was found to be 3 J inches thick with 544 annual rings 

 (counted under the microscope) : an annual ring consisting of one vessel 

 and one cell of wood-parenchyma in a radial direction. This was in a 

 sub-Arctic zone. The roots, as is the case in dry soils, attain consider- 

 able size, to search for a sufficient supply of water ; while nitrifying 

 bacteria are greatly reduced in quantity in consequence of the soil tem- 

 perature being low. 



The most northern of all latitudes where plants can grow at all are 

 the Arctic Tundras, where all flowering plants cease to exist, and 

 nothiug but mosses and lichens can flourish as the result of natural 

 selection. 



Enough has now been said to show that " natural selection " stands 

 for a phenomenon of plant life which may be witnessed everywhere. It 

 means the Survival of the Best-adapted under the Circumstances, in the 

 Struggle for Life, either in competition with other plants, or with a more 

 or less inhospitable environment. 



In all cases the explanation of the survival of the best adapted is 

 because such happen to be more suitable to enable them to maintain the 

 struggle. 



Lastly, such adaptations have always arisen through the Besponsive 

 Bower of Brotoplasm and the Nucleus. These together construct cells, 

 of which tissues are made, out of which organs are built up which are 

 best in harmony with the external conditions of life. 



Natural selection, therefore, has nothing to do with the origin of 

 species ; this supposed function is really solely and completely secured 

 by self-adaptation to the conditions of life ; but it has much to do with 

 the distribution of species all over the world. 



Postscript.- — Since the above lecture was in type, Mr. Druery has 

 called my attention to his experience with ferns, and observes : " Given 

 a pan of variable seedling plants, such variations as involve smaller size 

 and smaller area of foliage surface are injurious, detrimental, and 

 destructive, when they occur associated with other variations in the same 

 species, but of opposite kind ; the result being that the robuster variants 

 overgrow and eventually starve out the smaller by depriving them of 

 root- room and light." 



The reader will perceive that this is only another instance of natural 

 selection, as above explained, applied to seedlings. " Size," per se, is not 

 injurious; for where can the line be drawn? Had still more robust 

 plants been present in the pan, then those alluded to as survivors would 

 have perished in their turn. 



What I take Darwin to have meant, was some variation injurious to 

 the plant itself, irrespective of others ; comparable, e.g., to a child 

 unhealthy from its birth, or other of Malthus' causes of death in human 

 beings. It was a purely imaginary hypothesis to suggest such "injurious 

 variations " of structure. 



