78 PRESIDENTIAL ADDRESS SECTION C. 



later systems, that of Warming has become the best known. He 

 classified plants according to their water requirements, and his 

 terms "hydrophyte," "mesophyte," and "xerophyte" have become 

 familiar to every student of elementary Botany. Raunkiaer devised 

 an interesting system by using, as his main basis of classification, 

 the reaction of plants to the adverse season, a single factor which 

 influences very greatly their general life history and growth forms. 

 He also introduced a useful statistical method of comparing dif- 

 ferent climatic areas by estimating their agreement with or diverg- 

 ence from a "normal biological spectrum" for the whole world's 

 flora. I have elsewhere applied his system to the flora of Natal. 



The systems of Clements, Drude, and others each have points 

 of interest, but time does not permit of further reference to them. 

 All these systems agree in taking as the main basis of classification 

 the plant's reaction to inorganic environmental factors. Those 

 who have investigated the vegetation of their areas from the purely 

 morphological or static standpoint without troubling about the 

 developmental aspect, seek first of all to determine each plant's 

 water requirements, soil requirements, etc. Those, on the other 

 hand, who are keenly interested in the life histories of the plant 

 communities not only try to assign each plant to its proper com- 

 munity as determined by habitat but, in the field, habitually ask 

 themselves the questions, "What is this plant's exact place in the 

 plant succession V "Does it tend to be suppressed by or to suppress 

 other plants?" and so on. It seems to me, therefore, that the 

 time is ripe for the introduction of a scheme of classification based 

 entirely on plant succession. Such a system takes into account not 

 only the inorganic but also the living environment, that is, the 

 plant's relationship to other plants, in" a way that no other system 

 does. It also, however, reflects the plants' response to other habitat 

 factors as well, and not only a single master factor but them all 

 collectively. It will be necessary to introduce one or two terms. 

 Ecological nomenclature has been held up to scorn by more than 

 one botanical author, but it is perfectly clear that for new ideas 

 we must have new and definite terms, and we need not worry over 

 much about those who will not take the trouble to understand 

 them. 



All plants belong either to early or later stages of the plant 

 succession. For the former class the term "pioneer" is convenient 

 enough but for the plants which follow after the pioneers— there 

 is no good English term (I have elsewhere called them "subsequent 

 species"). To bring these two classes into line with other life- 

 forms we may use terms derived from the Greek, namely, "Prodo- 

 phytes" and "Hepophytes." Prodophytes are primitive colonising 

 species, which appear early in the plant succession, while Hepo- 

 phytes are species which require to have the way prepared for them, 

 and, therefore, appear later in the plant succession. 



Further subdivision of these two classes is a very simple matter. 

 It consists in determining the unit plant succession or "sere" to 



* Bews, J. W. " The Growth Forms of Natal Plants." Trans. Boy. 

 Soc. of S. Africa, V, 1916. 



