22 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



It is a minute annual belonging to the Flax family, with tiny flowers. 

 A genus of the Sedum family, Tillaea muscosa (1-2 inches) is a dweller 

 on sand, a minute, slightly succulent annual. The stem is only 1-2 

 inches high. Cicendia pusilla (1-2 inches) is a tiny member of the 

 Gentian family, occurring on sandy commons in Jersey. Many others 

 might be mentioned. 



Of course many plants often get starved, but do not lose all at 

 once the power of growing into larger plants, when plenty of water 

 and a good soil are present. Thus, a plant of the Silverweed (Potentilla 

 anserina) growing on a dry roadside had leaves 2 J inches long. One 

 half of this plant was transferred to a garden and supplied with an 

 abundance of water, being also slightly shaded. It ceased to develop 

 the silvery hairs on the upper surface, always present in strong sun- 

 light and dry situations. It now bore leaves a foot and a half in 

 length and 5 inches across from tip to tip of the leaflets. 



But the species mentioned above have become habituated to a 

 poor soil and impoverishment, and are not known by systematists 

 as exceeding the heights as given by Hooker, or the inches mentioned 

 above ; these are therefore included in the specific characters. 



A common effect of drought is the arrest of branches, whereby they 

 become spines, as in our Furze {Ulex) and the Needle-furze (Genista 

 anglica). The leaves also may become reduced to a rigid, pointed and 

 needle-like form, as occurs in Heaths and in Junipers. 



That this is the result of a want of water is shown by the fact 

 that if the seeds of the spiny restharrow (Ononis spinosa) be sown in 

 soil kept permanently wet the plants grow up with much reduced 

 needle-like spines in the first year, but in the second they grow out 

 into leafy and flower-bearing branches. Then it resembles the " arm- 

 less " species 0. inermis, found wild on better soils than that of 

 hard roadsides. 



In dry tropical countries there are the so-called Thorn-forests, 

 as spinescence is the prevailing feature. Similarly the Cactus family 

 has the leaves reduced to spines in the members growing on the 

 Mexican deserts. 



The needle-like form, as of leaves of Junipers &c., may take on a 

 still more degraded type, so that the leaves become as it were minute 

 scales pressed flat against the shoot. The Junipers often have both 

 kinds on the same plant, but the first to be formed is the longer, 

 spinescent form, the later, the minute, non-spiny one. This type 

 is familiar in the Ling (Calluna vulgaris) as compared with the Heaths 

 (Erica). It is seen in our shrubberies in the Thujas and Cjrpress, as well 

 as so-caUed Retinosporas. Indeed, our Speedwells are represented 

 by high mountain forms in New Zealand which take on a similar 

 form in the dry altitudes, just as our Lycopodiums or Club-mosses 

 prevail on Snowdon, the branches being " clothed " with minute, 

 scale-like leaves. Lastly, leaves may vanish altogether. This is the 

 case with our Broom, in which the green stems and branches now 

 undertake the physiological functions of leaves. 



