328 JOUENAL OF THE ROYAL HORTICULTURAL SOCIETY. 



simply the result of a deficiency of water, for if the Rest-harrow be 

 grown in moist earth and air its spines soon cease to be formed. 



Another type of foliage in dry regions is the " Ericoidal " or Heath- 

 like form. The leaf consists of a small narrow blade, more or less 

 pointed. In South Africa, more especially on the western side, Heaths 

 abound ; but in Australia, where similar conditions occur, Epacris 

 "represents" Heaths by assuming a very similar appearance. Indeed, 

 many other plants there, of quite different families, have a similar Heath- 

 like foliage. 



Mountainous Types. — One of the forms of foliage assumed by plants 

 of widely different families in far- distant parts of the world is the 

 " Cupressoidal " or Cypress-like foliage. The leaves are almost micro- 

 scopically minute, and closely adpressed against the branch. The 

 common Thuyas, Eetinosporas, and Junipers of our shrubberies, whether 

 from Japan or California, are examples. It is mimicked by our own 

 Ling growing with heaths. It occurs in the Clubmosses on Snowdon, 

 and some most remarkable mountain forms of Veronica in New Zealand 

 possess it as well. As drought appears to be one of the direct causes of 

 this diminished type of foliage, it is not surprising to find it mimicked in 

 the African deserts by Salsola Pachoi, See. So too, in the Antarctic 

 regions, it is exactly paralleled by that of Drapetes muscosa (ThymelaceBp), 

 Bolax Glebaria (Umbellifer?e), Lyallia kerguellcnsis (Caryophyllefp), 

 and Forstera clavigera (Stylideje). 



Muscoidal Type. — This is one of the extreme forms of high Alpine as 

 well as of Arctic and Antarctic regions. Besides some sf)ecies of Veronica 

 in New Zealand mountains, there are Saxifraga hryoides, S. muscoides, 

 Gherleria sedoides, Silene acaulis, Sec. Again, Bolax Glebaria (Umbel- 

 lifer8e),of the Falkland Islands, is mimicked by species of Acantliophyllum 

 (Caryophylletie) in x\fghanistan, and by Haastia (Compositje) in New 

 Zealand. 



A gradual reduction may thus be seen from the long and pointed leaf 

 of a Heath to the short and pointed one of Juniper. Then, the point is 

 suppressed and the Cupressoidal type is obtained. These two last-named 

 forms often occur on the same bush, as of Junipers, Retinosporas, &c. ; 

 the more pointed form, being the younger on the bush, corresponding to 

 the earlier condition in point of evolution. Lastly, the Cupressoidal 

 leaf is still further reduced, and a form is reached resembling that of 

 Salicornia. 



Linear Types. — When plants grow in massive tufts or are crowded 

 socially, so that the blades of the leaves are compelled to stand erect, 

 they take on very much the same form. A grass-leaf may be regarded as 

 the type. This is closely imitated by the Grass-leaved Pea {Lathy rus 

 A'issoZm), w^hich grows among grass. The same linear form is seen in 

 Pinks, Carnations, and Thrift. 



In all cases the anatomy corresponds with the form ; in that, while 

 in broad and horizontally situated leaves the stomates are altogether or 

 mostly on the underside, they are equally distributed on both sides 

 of erect-growing leaves. It reveals an obvious fact, that the form and 

 structure of such erect leaves, as compared with broader and horizontal 

 blades, is simply the outcome of the position which they are compelled to 



