202 TRANSACTIONS OF THE 



attained in light soils, we have a confirmation of the views here 

 advanced. The tap-root of the dock constitutes its title to a place 

 in this division. 



III. Speaking generally, plants growing in dry situations are 

 more freely supplied with hairs than those which frequent wet 

 places. According to Haeckel, if a plant be removed from moist 

 to dry soil, it becomes more hairy ; the end gained by these hairs 

 being to obtain a supply of moisture from the atmosphere, for 

 which there is greater need in a dry locality. The dead-nettle, 

 borage, mint, and rock-rose are familiar examples of this. Some 

 species of poppy, too, become covered with stiff hairs, particularly 

 on the seed vessel, and their leaves become cut up into segments 

 in a pinnatifid manner, simulating thistle leaves, if grown in dry 

 soil. Papaver hyhridum and P. argemone exhibit this markedly ; 

 the setose character of the seed vessel coming of use also to help 

 in disseminating the seed, by catching the fur of passing animals, 

 so that the seeds are shaken out of their capsule. Similar hairs, 

 correlated to a liking for dry situations, are observed in many 

 species of Fumariaceae, Cruciferae, Boraginaceae, Solanaceae, 

 Caryophyllaceae, and Malvaceae. Many of the last named order 

 are remarkable for their curiously forked hairs. They grow in 

 dry soil. To this order the cotton plant belongs, and it is not 

 improbable, in view of such facts as we have been considering, 

 that the hairs on the seed of this plant, and the hairy pappus on 

 the fruit of many compositae (down of thistle, seed of dandelion, 

 etc.), may have been acquired during long habituation to arid 

 conditions, although in the present condition of the plants, these 

 processes of hairs are directly related to disseminating the seed. 

 The fact that the cotton plant is not now confined to hot, dry 

 regions, the wet habitat of the cotton-grass, and a few other facts, 

 would appear, however, to render this theory doubtful. 



In the second class are placed those plants which, from being 

 provided with formidable weapons of defence, are best capable of 

 maintaining their ground against man ; thorny, prickly, and 

 stinging plants, abounding near the haunts of mankind in spite of 

 man's enmity; probably doing so in virtue of those qualities which 

 recommend the thistle as the national emblem of Scotland, viz., 

 that no one touches them with impunity. But there is a reason 

 why plants in poor soil should be of this jaggy character. 



