114 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



massive, and fleshy character. This occurs in several distinct families of 

 plants. 



This fonn of stem is particularly characteristic of members of the 

 family ( '(tc(tu-c<<\ such as of species of the genera Cactus, Cereus, &c. 

 recurring in the dry rocky regions of Mexico; but only a single plant 

 of this order (llhipsalis) is found in South Africa. Instead of this 

 family certain genera of others represent the Cactacece, as Euphorbia 

 (Euphorbiacc(c), Stapelia (Asclepiadacca), Adenium (Apocynacea), Kleinia 

 (Composite), &c. 



It is instructive to pass through the "Cactus House" (No. V.) in the 

 Kew Gardens ; for if a visitor look only at the plants, and not at their 

 labels, he will not know when he has passed the group of Euphorbias and 

 is gazing on members of the Cactacece. 



The fleshy type is by no means confined to the above-named genera, 

 for an ally of our groundsel of the order Composite?, is represented by a 

 long and Heshy-stemmed species (Senecio Johnstonii), sometimes growing 

 twenty feet in height. 



Those massive fleshy stems are well adapted for storing up water. 

 On the exterior there is a dense chlorophyll-palisade zone included within 

 an epidermis with a very thick cuticle. The greater part of the interior 

 is occupied by the cortex, consisting of large thin-walled cells in which 

 an inspissated water is kept. It is often milky, as in Euphorbias, or 

 gummy &0., so that the chance of loss of water by transpiration is much 

 reduced. 



Besides these aerial stems, some plants store up water in subterranean 

 stem-structures. 



The commonest in South Africa are the bulbs and corms of the 

 numerous monocotyledons which give so remarkable and characteristic a 

 feature to the flora of the Cape. The inner scales, besides being reservoirs 

 of food, also retain water. In the excessively hot deserts of North Africa 

 some bulbs, as of Allium Cramer i, have the outer scales of a dense, 

 almost woody character, thereby protecting the inner water-holding scales 

 from the intense heat of the sand. 



The genus Oxalis has a very large number of species at the Cape, one 

 of which, 0. cernua, was introduced into Malta in 1801. From that time 

 till the present it has spread more or less through the whole length, 

 north and south, of the Mediterranean regions. It possesses a remark- 

 able instrument for storing water. Growing among loose rubble, it sends 

 downwards a long slender rhizome till it becomes almost thread-like. It 

 bears minute bulbs and adventitious roots. At the extreme tip of this 

 thread it suddenly swells into a slender rod, two or three inches in length. 

 This stores up water. It finally bears a bulb at the actual end. No doubt 

 this is supplied with the water for growth, as soon as it germinates after 

 the dry season is over, 



In endeavouring to discover the immediate cause of the origin of 

 win. r storage tissues generally (for we shall find that leaves often 

 P098688 them) I would suggest that it is primarily due to the accumula- 

 tion of water within the plant, in consequence of the arrest of tran- 

 spiration. This latter function is in turn greatly impeded by the forma- 

 tion of a thick and often waxy cuticle, as well as by a dense clothing of 



