110 



the rachis of the common ash is furnished with a groove on its 

 upper surface which receives and absorbs moisture for several 

 days after a fall of rain. On the under surface of the leaves of 

 the alpine rose (Rhododendron) there are discoid glands sunk in 

 little hollows. When drops of rain fall the water soaks, by the 

 action of the hairs, to the under side of the leaf. It is then taken 

 up by the glands and absorbed by the plant. As soon as the 

 leaves become dry again the glands become covered with a dry 

 crust, and they thus prevent too great evaporation. Absorptive 

 cavities and cups are also found at the base of the leaves of the 

 Aspen, but possibly the most remarkable are the structures 

 adapted for absorption on the leaves of a group of saxifrages. In 

 one species {Saxijraga Aizoon) the leaves have little depressions 

 upon their upper surface behind the apex. One of these 

 depressions occurs in the middle of each tooth. In order to pre- 

 vent the loss of moisture each depression is provided with an 

 incrustation of carbonate of lime forming a stopper which fills the 

 entire cavity. Further, the crust of lime is ingeniously held in 

 place by a series of peculiar plugs. When rain or dew falls on 

 a saxifrage the water soaks under the crust of lime and diffusing 

 itself there is taken up by the absorption-cells at the bottom of 

 the depression. In dry weather the crust is appressed to the 

 cavity and impedes the evaporation of water. Somewhat similar 

 incrustations of lime are found on the leaves of plants growing 

 on the arid ground of steppes and deserts, but time will not per- 

 mit of a detailed account of these. 



Lime=loving and Lime=shunning Plants. 



It has been long recognised that soils containing a com- 

 paratively large proportion of lime are remarkable for the presence 

 of certain species of plants. This is within the common 

 experience of field botanists everywhere. Examples of the lime- 

 loving or calcicole species occurring on calcareous soils in this 

 district are discussed by Mr. Munn Rankin and the Rev. E. F. 

 Linton in the " Bournemouth Handbook of Natural History. " 

 Briefly stated, ash woods are characteristic trees in the chalk dis- 

 trict in the south with natural beechwoods on the escarpments 

 and valley sides. Other trees more or less associated on lime soils 

 are the pedunculated oak. The smaller trees and shrubs forming 

 the " shrub-layer" consist of the spindle tree, the blackthorn, 

 various roses, briars, dog wood, elder and the hazel. What is 

 known amongst ecologists as the "carpet " vegetation is a rich 

 one, and contains sheets of the dog mercury, primroses, wood 

 sanicle, violets and wild strawberry. The orchids, according to 

 Mr. Rankin, " are perhaps the greatest botanical charm of the 

 carpet association on chalk." "The grass lands (Mr. Rankin 

 continues) have open downs covered with sheep pasture. The 

 turf presents a great variety of colour according to the season. 

 Early summer finds it decked with masses of the rich blues and 

 heliotropes of the milkworts, the orange and yellow of lady's 



