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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



occur anywhere within the plant, or even externally as on the Ice-plant 

 (Mesembryanthemum crystallinum) as swollen globular hairs, filled with 

 fluid. In many plants the storage tissues are not very obvious from 

 without, as they may consist of layers of cells within the leaves, or in the 

 cortex or pith of the stems or in the roots, or again in the scales of bulbs, &c. 

 They become more conspicuous in all the numerous fleshy-stemmed or 

 leaded plants, such as of the families Cactacece, Crassulacece, Ascle- 

 piadacece, Euphorbiacece, &c. 



As this feature is thus found in families of no affinity, but only in 

 plants growing under similar climatic and " edaphic " * conditions, water- 

 storage adaptations afford another of the innumerable coincidences which 

 prove — even if there were no experimental evidence in corroboration of 

 it — that they are the result of a direct response to the influences of the 

 environment. 



It may be added that many plants of maritime or saline regions, as 

 salt-marshes, put on precisely similar structures, such as those of the 

 Samphire and Marsh Samphire, because they are physiologically xero- 

 phytic.t 



As an example of trees being provided with water-storage tissues is- 

 the Baobab (Adansonia digitata) of Africa. It has an enormous trunk, 

 but the woody fibres are of a spongy texture for storing water. 



There is another species in Australia (A. Greg or ii) as well as the 

 Bottle-tree (Sterculia rupestris), so called from its shape. These have 

 undoubtedly and independently acquired the same swollen form of trunk 

 by living under similar conditions of life. 



The two above-mentioned species of Adansonia — one in Africa, the 

 other in Australia — are examples of the fact that there are many families 

 possessing the same genera in these two continents, but there is not a 

 single species common to both. 



North African and other Deserts. 



Passing into the temperate but still warm regions with but little rain, 

 wc find many plants have very similar features, which have originated 

 in response, or in adaptation, to the surrounding conditions. They 

 only grow in the " wadis," or dry watercourses, below which water remains- 

 at varying depths. To secure it the roots grow proportionately long, 

 extending to even 40 feet in the case of the Narras plant (of the Cucumber 

 family) of Damaraland. 



Above ground there is always a great suppression of leaf surface, the 

 energies of the plant being directed to the reduction of any loss of water 

 by transpiration. 



As the leaves are small, the diminution of the usual assimilative 

 tissue (the so-called palisade cells) in area is compensated for by an 

 increase in thickness, the number of layers being increased. 



The epidermis is protected by a thick cuticle, often having a layer of 

 * A word coined to signify the influences of the soil. 



f At Hud Xauheim, where salt springs and marshy ground saturated more or less 

 with salt occurs, there are numerous plants of a " saline " nature. Amongst them 

 is an abundiince of l'lantago maritivia. As that place is situated some 200 miles from 

 the nearest coast, it raises the question whether P. maritivia may not be a saline 

 form of 1'. Coronopits, which it most nearly resembles, and so evolved on the spot. 



