GROWTH FORMS. 17 
growth-forms of its members, this term being explained below; and 
a plant-association, though resembling in general appearance any 
other association forming a part of the formation, is distinguished 
by possessing a different combination of species. 
In the case of the farm the distinguishing forms of the leading 
members of the artificial plant-formations stand out clearly. The 
grass form, the swollen-root form, and the annual-cereal form are 
all special plant-forms (growth-forms) which can maintain that 
form—and this is of prime importance—only under certain definite 
conditions, which the farmer of his own accord supplies. 
Thus plants may be classified not merely according to floral 
structure and relationships, but according to their outward form, 
such form being the outward expression of the plants’ behaviour 
under the spur of their environment, and, indeed, determining 
their existence. This particular form of a plant is known as its 
growth-form or life-form, and it is all-important with regard to the 
plant’s behaviour as a living organism, but has little to do with its 
status as a species, this latter being a matter of genetic relation- 
ship. In short, the growth-form is a biological* conception, while 
the specific form is floristic and genetic. 
As an illustration of a growth-form, all tall trees with spreading 
branches may be cited as belonging to one growth-form, whereas 
there are thousands of species of such trees, belonging to hundreds 
of families. Or a tree may have a very slender pyramidal form, with 
the branches not spreading—eg., the Lombardy poplar (Populus 
fastigiata), or the rewarewa (Knightia excelsa). Such different growth- 
forms as that of the beautiful white Clematis indivisa, a tendril- 
climber (fig. 4), and that of the noble mountain-lily (Ranunculus 
Iyallix), a summer-green herb with great saucer-like leaves and a 
thick succulent underground stem (fig. 1), belong to the same 
“family ’—a term explained in Chapter XI. 
It is clear that the growth-form is an all-important matter to 
be considered in regard to the living plant, while a classification of 
plants according to their growth-forms must be a necessary pre- 
liminary to the study of vegetation. In other words, it would be of 
great advantage were definite terms available for use when seeking 
*In this book the term “biological” refers not ‘to all the phenomena of 
zoology and botany, but only to that portion of these sciences which deals 
more particularly with vital processes and the relation of the organism to its 
surroundings. 
2—Plants. 
