292 THE LIFE OF THE PLANT 



frequently answered this question in the afifirmative, but 

 we have had no occasion as yet to consider the whole 

 body of proof that exists in support of such a state- 

 ment. This proof is given first of all by geology. We 

 have already seen in our first lecture that the vegeta- 

 tion of our planet is not the same to-day as it was 

 in former geological epochs, and that the more remote 

 is the epoch investigated the simpler are its forms. 

 Waterweeds appear first, then mosses, later still 

 horse-tails, ferns and club-mosses — all spore-plants ; 

 eventually seed-plants appear, and of these the conifers 

 come first ; whereas the latest, the most complicated 

 and perfected in their organisation, are the dicotyledons, 

 which to-day predominate on our planet. Thus, in 

 course of time, to types already existing new types 

 of plants have been added which have overcome 

 them in point of numbers ; and, moreover, the simplest 

 have been followed by the more complex. As we 

 have already seen in our first lecture, this funda- 

 mental geological fact can be explained by two con- 

 tradictory hypotheses : either the new types were 

 formed anew, quite independently from those that 

 existed before them, or they have arisen from them by 

 means of transformation, and therefore are directly re- 

 lated to them. I call both of these theories hypotheses, 

 and we cannot repeat it too often, because the exponents 

 of the first theory have applied this term with re- 

 markable persistence and assurance to the second 

 theory alone, forgetting that the one they hold is as 

 much a hypothesis as the other ; that it is an arbitrary 

 interpretation and not a simple statement of fact. 



Let us try to estimate the relative merit of these two 

 hypotheses. Let us see which of them agrees the 

 better with reality, explains the greater number of 

 facts, meets fewer contradictions — ^in a word, satisfies 

 the better the conditions we have to require of every 

 scientific hypothesis. 



