Influence of Habitat on Plant Habit. 135 



the development of hairs is favoured ; this is au indirect confirma- 

 tion of the result of exposure. The researches of Wollny (14). 



A recent paper bv Keller (1")) ends with the conclusion that a 

 hair-covering-, or the rudiment of one, exists in almost all plants ; 

 this is the case with, for example, the young leaves of the ivy, 

 Aucuba, Magnolia, &c. If this is true, the hairy coat if useless 

 will vanish wiih maturity, but if of some advantag-e it will be 

 preserved. One miglit almost trace the stages of fixation ; for, m 

 Polygonum amphiluum, the hair-covering varies with the exposure 

 of the individual plant ; in Daucus carrota it may be gradually 

 reduced by cultivation ; but, in the common garden plant, 

 Cerastium tomentosum, the down persists even in the moisture of 

 the British Islands. 



Among.st the 230 species I found 9 wiiich were either of the 

 very thorny type of Sonchus spinosus or of that represent^id by Zilla 

 myagroides. All these, as one would expect, vide Linnaeus (19), 

 Stapf (16), fiubbock (17), Lothelier (18), Mittmann (19), &c., are 

 from dry and arid places. There is also some direct evidence, for 

 Rolfe states that pruning increases the number of spines (20), and 

 Ilenslow found that Ononis lost its spines when cultivated in 

 moist condition.s. 



Table IV. 

 AFTER THE SONCHUS SPINOSUS AND ZILLA TYPE. 



Lepidium, 15 ... Palestine 



Matthiola. 11 Greece and arid countries 



Oudneya Algerian Desert 



Farsetia linearis Egyptian Desert 



„ Aegyptiaca Egyptian Desert 



Sisymbrium, 17 ... ... .. Australia 



Zilla ... ... ... ... Egyptian Desert 



Delphinium, 10 Waste places, Dardanelles 



,„ anthoideum Sandy, dry places 



Another type of plant very common in South Africa has no 

 very good example in this country ; it may be called the Aptosimum 

 type. It is a low-growing densely branched tiny shrub, often not 

 more than a few inches in height, and forms a sort of matted 

 cushion well adapted to arid conditions. 



Belonging to this type. I found 7 species amongst the number 

 examined. 



