PERPETUATION OF LIVING BEINGS 91 



It is extremely difficult to estimate, in a proper way, the 

 importance and the working of the Conditions of Existence. 

 I do not think there were any of us who had the remotest 

 notion of properly estimating them until the publication 

 of Mr. Darwin's work, which has placed them before us 

 with remarkable clearness ; and I must endeavour, as far 

 as I can in my own fashion, to give you some notion of 

 how they work. We shall find it easiest to take a simple 

 case, and one as free as possible from every kind of com- 

 plication. 



I will suppose, therefore, that all the habitable part of 

 this globe the dry land, amounting to about 51,000,000 

 square miles, I will suppose that the whole of that dry 

 land has the same climate, and that it is composed of the 

 same kind of rock or soil, so that there will be the same 

 station everywhere ; we thus get rid of the peculiar in- 

 fluence of different climates and stations. I will then 

 imagine that there shall be but one organic being in the 

 world, and that shall be a plant. In this we start fair. 

 Its food is to be carbonic acid, water and ammonia, and the 

 saline matters in the soil, which are, by the supposition, 

 everywhere alike. We take one single plant, with no 

 opponents, no helpers, and no rivals ; it is to be a " fair 

 field, and no favour." Now, I will ask you to imagine 

 further that it shall be a plant which shall produce every 

 year fifty seeds, which is a very moderate number for a 

 plant to produce ; and that, by the action of the winds and 

 currents, these seeds shall be equally and gradually dis- 

 tributed over the whole surface of the land. I want you 

 now to trace out what will occur, and you will observe 

 that I am not talking fallaciously any more than a mathe- 

 matician does when he expounds his problem. If you 

 show that the conditions of your problem are such as may 

 actually occur in nature and do not transgress any of the 

 known laws of nature in working out your proposition, 

 then you are as safe in the conclusion you arrive at as is 

 the mathematician in arriving at the solution of his problem. 

 In science, the only way of getting rid of the complications 

 with which a subject of this kind is environed, is to work 

 in this deductive method. What will be the result, then ? 

 I will suppose that every plant requires one square foot of 

 ground to live upon ; and the result will be that, in the 

 course of nine years, the plant will have occupied every 

 single available spot in the whole globe ! I have chalked 



