94 Sutton, Notes on the Sandrinoham Flora. \\J[ 



Vict. Nat. 

 XXIX. 



between associations of plants ; where, as physical conditions 

 alter, where the factors determining the growth of vegetation 

 vary, now one side, now the other, gains advantage and 

 extends its range at the expense of its neighbour. 



According to Clements, the plant association (formation, &c.) 

 is to be regarded as a more or less complex organism, the result 

 of certain factors present within the given area, the principal of 

 these being the water content of the soil, humidity, light and 

 temperature — and all capable of measurement. Shortly, the 

 formation is the expression of a habitat, which term is exactly 

 equivalent to environment. It possesses functions and structure, 

 and passes through a cycle of development similar to that of a 

 plant. As the simplest illustration, take an area hitherto unoc- 

 cupied by plant life {open). An individual plant arises in this 

 area, its seed having migrated from a distance — the plant thus 

 must have mobility. This plant establishes itself and reproduces 

 itself (ecesis). Migration and ecesis constitute invasion. An 

 aggregation of individuals occurs, yielding the simplest associa- 

 tion — a grow/) in vegetation, the family ; further grouping of 

 these results in a community. Especially when more than one 

 species is taking possession of the ground, variety is given to 

 the association, zones and layers, &c., are formed, giving it 

 structure. According to the seasons it presents different appear- 

 ances or aspects. For the areas controlled by principal species, 

 but changing from aspect to aspect, Clements proposes the 

 term society. The primary divisions of a formation he would 

 call consociations or consocies, and would apply the term to 

 an area characterized by a fades (dominant species of the 

 formation). When the whole of a natural area is covered with 

 vegetation the formation is said to be a closed one, and its 

 stability is greater than ever before. But there is no stasis. 

 Change is always going on, competition still keen, and as the 

 factors vary other plants better suited to the changed conditions 

 invade the formation, and succession occurs. The final result 

 is generally the forest after a series of these successions. 



To those establishing collections of dried plants, some of the 

 suggestions of Clements in favour of formational herbaria may 

 be of interest. Instead of the usual grouping in genera and 

 families, he would have the plants arranged with regard to 

 their position in the formation. This certainly seems most 

 rational, and, as he says, permits of definite comparison 

 between vegetations occurring in different localities. Specimens 

 should, of course, show both flower and fruit, with the under- 

 ground parts present and as perfect as possible. The grouping 

 of the specimens should have respect to their time of appear- 

 ance, their abundance, their importance as constituting the 

 *' facies," and definite associations in the formation should also 



