1899] ON THE STUDY OF PLANT ASSOCIATIONS 113 



(3) To describe the life-conditions of each " formation," and the 

 forms of vegetation characteristic of it, — whether trees (with 

 evergreen, needle-shaped, or deciduous leaves), shrubs, grasses, 

 herbs (perennial or annual), thallophytes, etc. 



Grisebach (1872) brought out his great work " Die Vegetation der 

 Erde," in which he employs the same methods for the description of 

 the plant-life of the whole globe. For this purpose he drew up a 

 scheme of 54 plant-forms to indicate the characters of vegetation of 

 each " formation." His classification was still on the whole geographical, 

 for his " formations " were defined as subdivisions of the landscape 

 (" pflanzengeographische Gliederungen der Landschaft "), and his "forms" 

 as the adaptational forms of plant-life most conspicuous in the land- 

 scape. 



Eeiter (1885) modified Grisebach's scheme of plant-forms to 

 reconcile it with later research in plant oecology. But all such 

 classifications must remain more or less artificial, until we understand 

 more about the nature of these " adaptations." Experimental and 

 histological work on the subject, like that of Vesque, etc. (see List B), 

 must be the basis upon which a true classification can be raised. 



Drude (1888) introduced the terms now usually employed to 

 indicate the relative frequency of species in a plant " formation." The 

 term " social " is applied to the dominant species, whose individuals 

 are so numerous that they seem to cover the whole of the ground, e.g. 

 the heather on a moor. " Gregarious " plants are those which live in 

 groups or patches in a " formation," e.g. Anemone nemorosa in a wood. 

 The other terms " copiously intermixed," " sparsely intermixed," and 

 " solitary " explain themselves. Pound and Clements (1898) point out 

 how often the eye may be deceived with regard to the relative value 

 of the secondary species of a " formation," and they advocate the 

 actual counting of the individual plants within type plots. Blomqvist 

 (1879) for a similar purpose has attempted a graphic method of 

 representing the secondary species in a formation, by mapping typical 

 small areas on a large scale. 



Thus methods were becoming well-organised, and several important 

 applications of them had been attempted, — in this connection " Das 

 Pflanzenleben der Schweiz " (1879), by Dr. Christ should especially 

 be noted. 



But the term " formation " was found to be insufficiently defined, 

 and it came to have a different meaning with different authors. The 

 "formations" described as units by Grisebach (1872 and 1875) were 

 split up into finer and finer divisions according to the minuteness of 

 the study given to them. Thus Hult (1881) has described almost 

 fifty for Finland alone. To distinguish them he employed a system 

 of nomenclature which is now frequently adopted, where each 

 " formation " is called after the dominant species with the termination 



