STRUCTURE OF THE PLANT 33 



less complicated as the case may be, but always improv- 

 ing, i.e. adapting themselves to the conditions of their 

 existence. Then we see in those transitional forms real 

 stages of development, gradual steps towards perfec- 

 tion, towards the improvement of the organ necessary 

 to the plant. Only then will the theory of meta- 

 morphosis, admitted by the exponents of the opposite 

 theory, however obscure and metaphysical it may be 

 from their point of view, acquire perfectly real and 

 definite meaning. This metamorphosis is the expression 

 in space of what has taken place in time. Those thick, 

 colourless cotyledons as well as these bright perfumed 

 petals have been derived from the origin of the common 

 leaf, and have gradually adapted themselves to their new 

 functions ; and those intermediate, transitional forms are 

 nothing - but the surviving formal evidences of the 

 process of transformation. They are memorials which 

 enable us to build up the history of the vegetable world. 

 This is the reason of their being so precious to science. 

 But are we entitled to affirm that the vegetable world 

 has a history ? Geology answers in the affirmative, and 

 we have j ust studied an illustration of the fact. We have 

 seen that our ferns, horse-tails, and club-mosses are only 

 degenerate descendants of former mighty masters of the 

 soil ; degenerate forms, forced nowadays to hide them- 

 selves in the depths of forests, or at the bottom of 

 ravines, to escape from the aggressive denizens of the 

 vegetable world of to-day. This means that the earth 

 used to be inhabited by other plants, and that these 

 belonged to the simpler spore-plants, which have 

 receded before our more perfect seed-plants. Hence 

 the fact of metamorphosis, as well as many other 

 similar facts which we shall consider later on, on the 

 one hand, and geology on the other, prove that the 

 plant world has a history of its own, and therefore that 

 our question as to the origin of vegetable forms is 

 perfectly legitimate. 



