MOUNTAINS, HILLS, AND DRY PLACES 



243 



As a hill is ascended the temperature is 

 lowered by i F. for each 300 ft. Hence the 

 montane species of flowering plants require 

 a longer period of sunny weather before the 

 thermal constants demanded by each species 

 are respectively reached. The persistence of 

 moist conditions or rainfall may also retard 

 flowering to some extent, as also the effect 

 of exposure and the wind. All these circum- 

 stances contribute towards the generally late- 

 flowering seasons of the plants of the hillside, 

 a fact easily demonstrated by a comparison 

 between a lowland and an upland meadow; 

 and the well-known purple tint of the moors 

 late in the summer or in autumn is a familiar 

 illustration of this fact on a wide scale. 



The chalk hills of Boxhill and elsewhere 

 furnish an example of the early flowering of a 

 hillside plant, the Box. This may be due to 

 the close habit of growth of the Box, the 

 sheltered character of the habitat, and its 

 southern origin and distribution. The Hairy 

 Violet, another chalk species, like all the 

 Violets is early, flowering also in June. In 

 May the Rock Rose, Kidney Vetch, Clary, 

 and Sheep's Sorrel are in flower, all but the 

 last, it should be remarked, being chalk 

 plants. 



June, however, is the principal month for 

 the hillside plants to flower. Then we may 

 find the following: Touch-me-not, Rest Har- 

 row, Silky Mountain Vetch, Sainfoin, Drop- 

 wort, Oak-leaved Mountain Avens, Wild 

 Thyme, Musk Orchid, Fragrant Orchid, 

 Sheep's Fescue. Many of these, again, are 

 limestone or' chalk plants. In July, Musk 

 Mallow, Hare's Foot Trefoil, Salad Burnet, 

 Field Scabious, Ploughman's Spikenard, and 

 Cotton Thistle flower, and the Gentians do 

 not bloom till August. On the whole it is thus 

 to be noticed that hillside plants flower late. 



Duration of Hillside Plants. There are 

 several reasons why the duration of hillside 

 plants should be more or less uniform. In 

 the first place, the late flowering of the plants 

 of upland regions, which has already been 

 pointed out, necessitates this; for it is impos- 

 sible for plants that are subjected to conditions 

 prevalent in highland regions to mature in 

 the same manner as those that grow in the 

 lowlands. Hence it is that with a few excep- 

 tions the upland plants are perennial. They 

 form frequently wide associations, which are 

 generally made up of perennial plants, such as 

 Grasses, Sedges, Heaths, &c. 



At higher elevations there are not many 

 plants of annual or biennial duration ; for the 

 ground is not open or broken, but taken up 

 more or less continuously by plants of vigorous 

 dominant growth. Cotton Thistle, the com- 

 VOL. IV. 



inon Gentians, Touch-me-not, and Hare's 

 Foot Trefoil are annual or biennial. It is thus 

 clear that the hillside plants have adapted 

 themselves to perennial conditions as a result 

 of the factors that govern the upland floral 

 regions. 



The Pollination of Upland Plants. The 

 uplands consist largely of pastures, and there 

 is as a consequence a parallel between the 

 conditions for insect life on the hills and the 

 lowlands, where pastures are also predominant. 

 The hills are, in fact, as much alive with the 

 busy hum of the insects in spring and summer 

 as the lowland meadows. This may be seen, 

 indeed, in the existence of a large number of 

 insect pests that live as larvas upon the hillside 

 plants. 



The openness of the hillside contributes to 

 the prevalence of insect life, for insects can 

 wander at will unimpeded by any barriers as 

 in woodlands, or where the type of habitat is 

 restricted as in the case of a cornfield, a bog, 

 heath, &c. The hillside plants as a whole 

 have brilliantly-coloured flowers, conspicuous 

 and attractive, as Rock Rose, Marsh Mallow, 

 Kidney Vetch, Sainfoin, Field Scabious, Clary, 

 Musk Orchid, Fragrant Orchid, &c. 



Salad Burnet, Sheep's Sorrel, Sheep's Fes- 

 cue are pollinated by the agency of tin- wind. 



The Dispersal of Seeds of Hillside Plants. 

 The exposed nature of the uplands would at 

 first sight appear to be a factor in the dispersal 

 of hillside plants. As a matter of fact, upon 

 the uplands there are extensive associations of 

 a single species, such as Ling, Whortleberry. 

 These as a rule occupy the higher zones, win-re 

 the less dominant types are as a whole absent. 



There are, however, wide associations, as in 

 wet and dry meadows of Sedges, Rushes, 

 Grasses, &c. , at lower altitudes. Some of these 

 may grow in such association, as Matweed, 

 &c., as to exclude other types of plants with a 

 different growth-habit. But even here, usually 

 lower down there is a noticeable intermingling 

 of other species. Amongst those with seed- 

 dispersed by the wind are Weld, Rock Rose, 

 Hare's Foot Trefoil, Sainfoin, Dropwort, 

 Salad Burnet, Oak-leaved Mountain Avens, 

 Ploughman's Spikenard, Cotton Thistle, 

 Sheep's Sorrel, Musk Orchid, Fragrant Orchid, 

 Sheep's Fescue, and some of these are dis- 

 persed in part by their own mechanism to a 

 shorter distance. 



Some arc dispersed by animal agency, as 

 Dropwort, Field Scabious. The Hairy Violet 

 is assisted by ants in the dispersal of its seeds. 

 In Touch-me-not and Rest Harrow special 

 contractile tissue enables the seeds to be jerked 

 when ripe from the pod, as also in Kidney 

 Vetch. Silky Mountain Vetch, and Box. 



