MISCELLANEOUS PLANTS 



229 



(p. 19) that Sccevola as a genus has a characteristic inclination for a 

 littoral life (" neigung fur das Litoralleben "). This inclination is 

 well illustrated in the circumstance that many of the Australian 

 species are equally at home in arid inland districts and at the coast, 

 though very few are exclusively littoral in their station. The 

 adoption of a station at the coast does not necessarily involve a 

 wide range for a plant, the acquirement of buoyant qualities by the 

 fruit or by the seed being as a rule needed for a wide distribution. 

 In other words, the littoral plant must be suited for dispersal by 

 currents to ensure a wide range. Thus it may be safely assumed 

 that the five other species of Sccevola named by Krause (p. 19) as 

 the most typical strand plants have but slight capacity for dis- 

 tribution by currents, since they are all confined to Australia, and 

 four of them are only known from West Australia. The origin of 

 buoyancy in seeds is dealt with in detail in my book on Plant 

 Dispersal. Buoyancy whether of seed or fruit is quite accidental as 

 far as adaptation to dispersal is concerned. It is just as likely to 

 be developed in inland plants, especially where dry conditions pre- 

 vail ; and it is shown that in such cases, where the plants are xero- 

 phytes, they tend to gather at the coast. But it is only the littoral 

 station that determines its utility for dispersal, since it brings the 

 plant with buoyant seeds or fruits within the influence of the currents. 



In many strand floras there is an element composed of local 

 inland xerophilous plants, which, being at home in the neighbouring 

 dry districts of the interior, encroach" in places on the beach, but 

 through lack of fitness for dispersal by currents do not accompany 

 the other beach plants with buoyant seeds or fruits that extend 

 their ranges across the sea far beyond that particular locality. With 

 the exception of Sccevola Kcenigii, it is probable that nearly all the 

 Australian species of the genus that find their homes more or less 

 frequently on the beach belong to this category. The littoral flora 

 is liable to receive numerous accessions from the inland flora, where 

 the conditions of the interior favour the growth of xerophilous 

 plants. This I found to be especially the case in the Turks Islands, 

 where the plants growing away from the beaches are mostly xero- 

 phytes. So also on the Chilian beaches I found that the strand flora 

 contained numerous intruders from the neighbouring dry inland 

 regions (Plant Dispersal, p. 478). Schimper lays stress on the 

 inclusion in the Indo-Malayan strand flora (p. 197) of colonists from 

 sandy or stony places inland. Harshberger tells us how the numerous 

 xerophytes of the chaparral scrub of the arid interior of Mexico and 

 Texas descend to the plains that border the sea and extend along the 

 shores of the Gulf of Mexico (p. 660, etc.). . 



I have here gone far enough to indicate the nature of the problems 

 opened up when we recognise in Scwvola a genus eminently suited 

 for supplying strand species. We are now in a better position to 

 understand how the genus has come to furnish two of the limited 

 number of strand plants that are cosmopolitan, or semi-cosmopolitan, 

 in the warm regions of the globe, a considerable proportion when 

 we reflect that even including the plants of the mangrove formation 

 the total number would probably not exceed fifty. 



