THE IMPORTANCE OF HAIRS IN PLANT LIFE 83 



It is interesting to compare the structure of the same plant 

 growing in different situations. The Rest-Harrow is more thorny 

 in dry situations than in moist valleys, the Meadow-Sweet appears 

 to have almost entirely smooth leaves, when growing in damp 

 places, and to develop hairs on the leaves in drier soil. 



Much more accurate observation needs to be made on this 

 subject of the hairiness of plants. Although it may be stated 

 generally that plants belonging to dry situations are hairy, there 

 are many exceptions of which as yet no explanation is forth- 

 coming. Why are those Forget-me-nots which grow in damp 

 places hairy ? The reason may possibly be that they belong 

 to an order of plants which is conspicuously hairy. The Viper's 

 Bugloss, Borage, Alkanet are all strikingly so. Then the Water 

 Forget-me-nots and Comfrey, which also belong to damp situa- 

 tions, and might be expected to be smooth, are also hairy. 

 As a rule, structures of this kind are not necessarily affected 

 by facts of relationship. There are numerous instances of very 

 closely allied species, which differ in this character of hairiness 

 according to the situation in which they live. Another explana- 

 tion that is sometimes suggested is, that these hairy plants now 

 found in wet ground, as by streams, etc., at one time grew in 

 drier situations, and that they have not yet lost the hairy char- 

 acter which then was of use to them. It is impossible in the present 

 state of our knowledge to account for these differences. More 

 accurate observation of the same species under different con- 

 ditions is necessary, and one or two suggestions are now offered. 



Examine the leaves of plants growing by streams, or in marshy 

 places, such as the Meadow-Sweet, Ragged Robin, Cuckoo Flower, 

 Water Avens, Figwort, etc., and note whether they are hairy 

 or not. Compare them with other plants of the same species 

 growing in drier situations, as for instance in land which was 

 marshy but has been drained. 



Compare plants of the same species growing on hills and by 

 the seashore ; the common Erodium will be found in both these 

 habitats. Note the degree of hairiness. As a rule, plants growing 

 in both these localities are hairy, on account of the dryness of 

 the situation. Not only are plants by the seashore inclined to 

 be hairy, but they often have their leaves reduced to spines. 



