FORM AND SIZE OF PARTICLES EMPLOYED IN CONSTRUCTION OF PLANTS. 567 



gas and water begin and end in the manner best adapted to the given conditions; 

 while the pillars and beams are placed where something has to be protected, borne, 

 or prevented from bi-eaking down. 



Such structures, just like the buildings produced by the hand of man, convey 

 the idea of fitness of means to ends. Indeed, they often surpass mere human 

 creations in the suitability of their arrangement. It can hardly be invariably 

 said of man's designs that they are carried out in a way completely suited to the 

 requirements of the case; while no plant lives and maintains itself which is not 

 adapted to the given conditions of life in the most advantageous manner. The 

 most i-emarkable thing about it is that this adaptation in plants is not produced 

 directly by external influences, but that rather the individual portions assume the 

 most suitable form and position, even in their first rudiments and very early 

 stages of development; that is, at a time in Mdiich the forces acting outside the 

 plant can have no considerable influence in directly moulding its form. Such an 

 adaptation presupposes, however, a law of form; in other words, a plan of con- 

 struction, a plan concei'niug the division of space best suited to the future division 

 of labour, a plan of the most advantageous construction of the whole framework, 

 the most suitable position of the conducting and ventilating mechanisms, and much 

 besides, which will benefit the plant in the future. 



This supposition being forced upon us, the question arises as to whether it is 

 correct to speak of a constructive plan in plants. In the sense in which we speak 

 of the constructive plan of a house, certainly not. Plants are not l:)uilt accoi-ding 

 to a plan devised by themselves, but their oi-gans receive their definite form, as if 

 according to a prescribed law, from inward necessity, like the crystal whose shape 

 is dependent upon and founded in the chemical composition of the fluid from 

 which it is formed. But just as we can speak of the plan and elevation, of the 

 symmetrical arrangement, even of the plan of construction, of a crystal, equally 

 well can we speak of the plan of construction, or, if we prefer it, the law of form, 

 of growing plants. The plan of construction is given and traced out for every 

 plant by its specific constitution, and so far every species has its own plan quite 

 independently of the external influences which it follows, indeed, is compelled to 

 follow, as long as the constitution is not altered. 



But by specific constitution we do not merely understand the chemical com- 

 position, the definite number of atoms, and their characteristic grouping into 

 molecules. We understand fux'ther the union of molecules in definite groups of a 

 higher order, which must be regulated in the plant body just as in the body of a 

 crystal. This arrangement of the molecules is characteristic, we must suppose, for 

 every species of plant; further, we must believe that the substance which is 

 associated with the growth of the molecular gi-oups, already present, is always 

 subordinated to the laws of symmetry prevailing there, and tliat this grouping is 

 not only specific, but also constant and invariable. 



When we speak of crystals, we do not mean to say that the processes in ques- 

 tion in them and in plants are identical. It is much more probable that there is 



