598 DERIVATIOX OF EXISTING SPECIES. 



similarly, their external form spontaneously, has been so fully met by the obser- 

 vations recorded in the last chapter that it is hardly necessary to deal with it 

 now at great length. I shall content myself with pointing out that it is impossible 

 to give a natural explanation of such a phenomenon. Every variation presupposes 

 a corresponding disturbance; for the acquirement of any new structural character 

 the plan of construction must undergo some fundamental alteration. The naturalist 

 is unable to grapple with the phrases " internal causes ", " internal force ", " force 

 of transformation ", " tendency to diiFerentiate ", " principle of progressive trans- 

 formation ", when attempting to explain variation in a natural manner upon 

 mechanical principles. Nor is the likening of this transformation to the meta- 

 morphosis which every individual passes through at various periods of its existence 

 at all to the point, since metamorphosis repeats itself with great constancy in 

 every species according to the plan of construction which is laid down in the 

 specific constitution of the protoplasm. That the protoplasm of any species should, 

 in the absence of any impulse or stimulus from outside, be able spontaneously to 

 alter its plan of construction contradicts all our experience of the normal action 

 of natural forces. Even should we conceive vital force, the dormant energy of 

 the protoplasm, to be converted into an active form, it could only give rise to 

 movements which have their origin in the specific constitution of the protoplasm. 



And now we come to the assumption that this inherent force of transformation 

 is a progressive one, that it leads to a higher or more perfect development. But 

 what is to be regarded as a higher development amongst plants? A tree with 

 its brightly coloured flowers and luscious fruits seems more highly developed to 

 the non-botanist than a low herb with inconspicuous flowers, or than the green 

 filaments of a Spirogyra destitute of flowers. The supporters of the theory under 

 discussion assert that the highest development is that which exhibits the greatest 

 complexity of form, and in which division of labour is carried fm'thest. And in 

 this assertion they do not essentially difi'er from the popular \4ew. Complexity 

 of form and division of labour are undoubtedly carried further in an Apple-tree 

 than in the Spirogyra of the ponds and ditches. But it must not be forgotten 

 that the difiTerentiation of a plant-body into various tissues, the production of 

 wood, bast, and cork in its stem, of cuticle, stomates, and hairs on its leaves, of 

 various colouring-matters and aromatic substances in its petals, and of sweet juices 

 in its fruits, stands in harmonious relation to the environment of the plant in 

 question. Change the conditions, and imagine the Apple-tree submerged in a pond; 

 it is no longer in harmony with its surroundings, its complexity of tissues, its 

 wood, stomates, &c., are not so well adapted for these conditions as are the Spiro- 

 gyras and Water-weeds equipped with organs of another type. The size of a 

 plant is often — in the popular estimate — the indication of its high organization. 

 A big plant gives the impression of possessing a more perfect development than 

 a small one. But this criterion leads to no satisfactory result; it is sufficient to 

 instance the case of certain huge sea-weeds {Macrocystis) of the southern seas, which 

 exceed our greatest forest trees in height. ^Mauy Thallophytes, only visible under 



