82 PLANT PHYSIOLOGY 



logy ' we have taken a step in the right direction, and trust that our treatment 

 of the subject will demonstrate the numerous gaps in our knowledge that have 

 up till now existed, and at the same time lead to their being filled up. Indeed, 

 there are still many problems unsolved even unformulated for much of the 

 subject has been treated of only descriptively. We will commence with an 

 essentially descriptive treatment, and endeavour to make ourselves acquainted 

 first of all with the phenomena of growth (Lectures XX XXIII). Afterwards 

 we will endeavour to determine the external (Lectures XXIV, XXV), and 

 internal (Lecture XXVI), factors concerned in growth, and finally discuss the 

 phenomena of development (Lectures XXVII, XXVIII), reproduction, heredity 

 (Lect. XXIX), variation and species formation (Lect. XXX). 



Before beginning our studies, however, we will attempt to justify our 

 position in devoting this section to the ' form ' of the plant, and so to a certain 

 extent contrasting the ' form ' of the plant with ' the materials ' of which it is 

 made, and which we have already considered. If the introduction to SACHS'S 

 famous treatise (Ueber Stoff und Form, 1880) be studied, our action in so 

 doing may appear somewhat open to criticism. SACHS says ' plant morphology 

 often suffers the misfortune that the form of the plant is looked at without any 

 regard being had to its material characteristics '. 'A consideration of its 

 material characteristics ' is most certainly essential, ' for it is in these only that 

 the causes of its form may be sought for.' ' Just as the form of a drop of water 

 or of a crystal is the necessary result of forces which bring the material in 

 question under the influence of its environment, so also organic form can only 

 be the outward expression of forces which transport materials, which make 

 themselves apparent in the plant substance.' 



Valuable as are the opinions which SACHS has put forward in this treatise, 

 with the view of aiding in a revival of the subject of ' causal morphology ', we 

 are nevertheless unable to agree entirely with the sentiments expressed in the 

 sentences quoted. We cannot find that SACHS, or indeed any other author, 

 has succeeded in referring the form of an organ to its material characteristics, 

 and, keeping before our eyes the phenomena of non-living nature, we must 

 confess that it is improbable that anything of the kind is ever likely to be 

 established. Many chemical compounds have characteristic crystalline forms, 

 and often these forms serve for the diagnosis of different bodies ; still the same 

 form may be built up out of different materials. Thus it would be in the highest 

 degree dangerous to refer the different forms of leaves to differences in the 

 materials composing them. But even if that were possible, we must still, as 

 in mineralogy, treat of the form of the plant by itself. Even although it were 

 possible to prove that a definite form results from the presence of a definite 

 material characteristic, still we should not know why it was so, any more than 

 we should know why calcium oxalate crystallizes in a tetragonal form when 

 three molecules of water are present, and in the monosymmetrical form when 

 there is only one. Nowadays, when it is as yet impossible to refer form to 

 chemical peculiarities, a section treating of ' change of form ' appears to us 

 quite essential. 



In discussing change of form in the plant, it would lead us away from our 

 subject were we to consider also the corresponding researches in the domain 

 of Zoology (Developmental mechanics) ; but the attempt must soon, how r ever, 

 be made, since, in spite of the agreement in fundamentals, there are still too 

 few points of contact in individual cases ; for the mode of development of the 

 typical animal differs widely from that of the typical plant. We must not, 

 however, fail to draw attention to the brief general exposition of the results 

 obtained in zoology, published by DRIESCH (1906). 



1. 32, after organisms read i. e. such as possess neither protoplasm nor 

 nucleus 



