18 THE POPULAR SCIENCE MONTHLY. 



Prof. Edward L. Youmans was, of all Americans I have known 

 or heard of, the one most able and most willing to help me. 

 Alike intellectually and morally, he had in the highest degrees 

 the traits conducive to success in diffusing the doctrines he es- 

 poused ; and from that time to this he has devoted his life 

 mainly to spreading throughout the United States the doctrine 

 of evolution. His love of wide generalizations had been shown 

 years before in lectures on such topics as the correlation of the 

 physical forces ; and from those who heard him I have gathered 

 that, aided by his unusual powers of exposition, the enthusiasm 

 which contemplation of the larger truths of science produced in 

 him was in a remarkable degree communicated to his hearers. 

 Such larger truths I have on many occasions observed are those 

 which he quickly seizes — ever passing at once through details 

 to lay hold of essentials ; and, having laid hold of them, he 

 clearly sets them forth afresh in his own way with added illus- 

 trations. But it is morally even more than intellectually that 

 he has proved himself a true missionary of advanced ideas. 

 Extremely energetic — so energetic that no one has been able to 

 check his overactivity — he has expended all his powers in ad- 

 vancing what he holds to be the truth ; and not only his powers 

 but his means. It has proved impossible to prevent him from in- 

 juring himself in health by his exertions ; and it has proved im- 

 possible to make him pay due regard to his personal interests. So 

 that toward the close of life he finds himself wrecked in body and 

 impoverished in estate by thirty years of devotion to high ends. 

 Among professed worshipers of humanity, who teach that human 

 welfare should be the dominant aim, I have not yet heard of one 

 whose sacrifices on behalf of humanity will bear comparison with 

 those of my friend." 



Though the volume containing this passage will not be pub- 

 lished until after my death, I am very willing that this tribute of 

 admiration to my late friend should be made public now. 



I am, faithfully yours, Herbert Spencer. 



A committee of the British Association is charged with the collection of infor- 

 mation respecting the disappearance or threatened disappearance of rare plants. 

 While instances of complete extinction of any species within recent times may be 

 rare, there are more of local extinction or of apparent extinction for a time, and 

 the cases of threatened extinction are numerous enough to he alarming. A potent 

 factor in the changes that have taken place is " the injudicious action of botanists 

 themselves, and of botanical exchange clubs. The 'dealer' and 'collector' also 

 figure largely in the process, while tourists are not responsible for much damage 

 except indirectly by patronizing dealers. It is too often forgotten that the very 

 rarity of a plant is the sign, and in great degree also the measure, of the acuteness 

 of its struggle for existence, and that, when a plant is in unstable equilibrium with 

 its environment, a small disturbance may have di?proportionately great effects." 



