PRESIDENTIAL ADDRESS SECTION C. 79 1 



which they belong, e.g., Prodophytes in the xerosere (Xeroprodo- 

 phytes) colonise bare surfaces and dry situations. Prodophytes in 

 the psammosere (Psammoprodophytes) colonise sand. Prodophytes 

 in the hydrosere (Hydroprodophytes) are the aquatic and marsh 

 plants. Corresponding to each of those we have Xerohepophytes, 

 Psammohepophytes, Hydrohepophytes. Recently a scheme of work 

 has been planned and to a certain extent has been carried out at 

 the Natal University College, consisting of a physiological — 

 anatomical comparison of typical prodophytes and hepophytes. The 

 work is still far from complete, and such results as have been 

 obtained have still to be checked in various ways, but the following 

 points may tentatively at least be put forward to illustrate the more, 

 important differences between the two classes : — 



1. Prodophyes have more abundant and varied means of repro- 

 duction, both vegetatively and by means of seed, than hepophytes. 

 Annual and biennial plants are usually pioneers, especially in 

 secondary successions (subseres). 



2. Prodophytes are adapted to more extreme conditions and 

 are therefore either xerophytic or hydrophytic. Hepophytes are 

 more mesophytic. Under very extreme conditions (of drought) the- 

 whole vegetation may be prodophytic. In that case the primitive 

 stage of the succession is also the final stage. 



3. Prodophytes are light-demanding and intolerant of shade. 

 Hepophytes are shade bearers or intolerant of full sunlight, at least 

 in their early seedling stages, though they often become more light, 

 demanding as they grow. 



4. Prodophytes are more low growing than the hepophytes 

 which belong to the same unit succession (sere). Many prodophytes 

 are creeping forms, while the hepophytes grow erect. 



5. Prodophytes are often more deep-rooted than the hepo- 

 phytes which belong to the same sere. 



6. The total number of prodophytic species is much smaller 

 than of hepophytic. The largest number of hepophytic species, 

 however, belong to intermediate rather than to final stages of the 

 plant succession. 



7. Prodophytes are more widely distributed geographically 

 than hepophytes. (See Bews, Annals of Botany, 1920, p. 287.) 



8. Prodophytes are somatically more plastic than hepophytes. 

 Individual species of prodophytes show a considerable degree of 

 variation in their structure and physiological behaviour, and are 

 found, therefore, under a wider range of environmental conditions, 

 than hepophytes. 



9. Prodophytes are influenced chiefly by the inorganic environ- 

 mental factors, though the microflora and fauna of the soil is doubt- 

 less of importance. As soon as the succession advances far enough 

 to bring the living environment (of other plants) into operation, 

 prodophytes are ousted. For hepophytes the living environment 

 is of the utmost importance. 



