114 PLANT HABITS AND HABITATS IN THE 



FEATURES OF ROOTS OF SOUTH AUSTRALIAN PLANTS. 



Whatever may be the reasons, there appears to be a comparatively 

 Umited range of variation in the types of roots developed in perennial 

 plants of South Australia, and possibly of Australia taken as a whole; 

 in herbaceous forms, however, such does not appear to be the case. 

 Thus there are herbaceous species with perennating fleshy roots of 

 various types, as well as those with roots that are fibrous, and the 

 latter may be various as to form, direction, and extent of their de- 

 velopment. As to the perennials of the state, an analogous condition 

 seems not to exist. The roots of perennial plants may be divided, as 

 to general development, into those which may be said to be specialized 

 and those which are generahzed. The former are either obligately 

 deeply penetrating or they are obligately shallowly placed. In certain 

 regions, as for example in southern Arizona, all three root-types are 

 to be found. To mention only one root-type, the obligate shallow form, 

 it may be said that this is associated in Arizona almost exclusively 

 with the quality of fleshiness in the species. In South Australia, on 

 the other hand, roots of this character appear to be quite wanting, or 

 at least they remain to be demonstrated. Possibly this is because of 

 the lack of fleshy perennials of a type analogous to the American cacti. 

 It therefore appears to be necessary to account for the absence of per- 

 ennials with water-storage capacity in South Australia in order to 

 account for the failure to develop obhgately shallow roots. Both of 

 these are certainly not without their difiiculties. 



It would appear to be puzzUng that herbaceous species with peren- 

 nating subterranean parts are developed in large numbers in a region 

 in which fleshy perennials do not occur. It does not seem improbable 

 that certain of the environmental conditions favorable to the growth 

 of the one may also be favorable to that of the other. Thus, the roots 

 of certain cacti, as mentioned in another place, require a well-aerated 

 soil as well as one that is suitably moist and of a fairly high tempera- 

 ture. In all cases moisture is a condition sine qua non of root-growth. 

 The optimum temperature for growth may vary as between different 

 fleshy perennials, but it remains to be shown that the same is true as 

 to the oxygen-supply. That, as a matter of fact, such fleshy plants 

 as various species of the cacti can live in parts of Australia, including 

 South Australia, is well known. So far as is known, also, these intro- 

 duced forms develop roots of a type characteristic of them in other 

 lands. In short, it can be said that the type of roots which develop 

 in the upper soil layers, and which do not normally attain to any con- 

 siderable depth in the soil, is quite wanting in South Australia, for 

 reasons which are not apparent. 



It is probable that a close study of the roots of the perennials would 

 show many with a well-developed tap-root and with an obligate, 

 deeply penetrating habit of growth. As a matter of fact, I saw but 



