CHAP, ii GROWTH-FORMS 3 



itself especially in the habit, and in the form and duration, of the nutritive 

 organs (in the structure of the foliage-leaf and of the whole vegetative 

 shoot, in the duration of life of the individual, and so forth), but shows 

 to a less extent in the reproductive organs. This subject leads us into 

 deep morphological, anatomical, 1 and physiological investigations ; it is 

 very difficult, yet very alluring ; but only in few cases can its problems 

 be satisfactorily solved at the present time. Thus we impinge upon the 

 problem of the origin of different species. 



But difficulty is imparted to the question under discussion by the 

 circumstance that, not only is a species changed in form by external 

 factors and capable of adapting itself to these, but each species is also 

 endowed with certain hereditary tendencies, which, for inherent but 

 unknown causes, evoke morphological characters that cannot be corre- 

 lated with the present environment and are consequently inexplicable. 

 These inherent tendencies, differing as they do according to systematic 

 affinity, render it possible for different species, in their evolution under 

 the influence of identical factors, to achieve the same object by the most 

 diverse methods. While one species may adapt itself to a dry habitat 

 by means of a dense coating of hairs, another may in the same circum- 

 stances produce not a single hair, but may elect to clothe itself with 

 a sheet of wax, or to reduce its foliage and assume a succulent stem, or 

 it may become ephemeral in its life-history. 



On the one hand, in very few families of flowering plants (e. g. Nym- 

 phaeaceae) have the different species assumed approximately the same 

 growth-form, or in other words acquired in harmony with the same 

 environment the same external form, and similar adaptations and habits 

 of life. As a rule, the members of a family differ widely from one another, 

 both in form and in their demands upon "the environment. On the other 

 hand, species belonging to families systematically wide apart may be 

 extraordinarily like one another in regard to the structural features of 

 the vegetation-shoot. A striking example of this is afforded by Cactaceae, 

 cactus-like species of Euphorbia and of Stapelia. These furnish an 

 admirable example of a single, marked growth-form which is clearly 

 adapted to definite external conditions, appearing in three families that 

 are distant in affinity (enharmonic convergence}. Another illustration 

 is seen in the case of Hydrocharis, Limnanthemum, and others, which 

 display so puzzling a likeness in form of their leaves to the Nymphaeaceae. 



The term growth-form used in this work nearly corresponds with 

 the term vegetative form employed by some botanists, but involves more 

 rigid scientific definition. The term vegetative form was introduced by 

 Grisebach and has been employed in literature in various senses, so that 

 it requires explanation. Within the same vegetative form were included 

 all those species that are more or less closely similar in design and appear- 

 ance, whether they be of close or very distant affinity. The design 



1 Anatomy, particularly stimulated by Haberlandt, has recently been greatly 

 enriched by numerous researches dealing with the question of the harmony between 

 structure and function or environment. Duval-Jouve (1875) nad already denned 

 work of this kind in the following words : ' L'objet de la presente etude est de 

 constater les principales dispositions des tissus dans les feuilles des Graminees, et 

 de determiner, autant que possible, le rapport de certaines dispositions avec les 

 fonctions imposees par le milieu.' 



B 2 



