DISTRIBUTION OP THE RAINFALL. 289 



required. But fresh supplies varying in quantity with the requisites 

 of the seedling, the sapling and the tree, and with the requisites of 

 the tree at the period of flowering, of the setting of the fruit, of the 

 maturing of the fruit, and of the casting of the seed, are needed. These 

 the parched land could not supply, neither could the snow covering 

 the mountain summit, nor the marsh in the valley below, though the 

 rain falling on the mountain side, with its excess drained off before 

 it could damage, and its supply from time to time renewed, might to 

 some extent determine the primary distribution of forests clothing 

 the mountain side ; and while other kinds of trees perished there, 

 they might find the conditions of their growth in the moister land 

 below, kept moist by the rainfall, and the drainage of the rainfall, 

 from a higher level, or on the banks of streamlets and rivers fed by 

 this rainfall and dependent thereon for their continuous flow. 



We need not to take up, in connection with this subject, the 

 question, Whence come the seeds ? But there is another question, 

 nearly akin to this, which suggests itself, and which finds in con- 

 nection with the subject under consideration a ready answer : Might 

 not other seeds besides those producing the forests also find their way 

 thither 1 They might and so might seeds of trees ; find their way to 

 plains where grow only herbs and grass ; and where now grow the 

 trees there may grass and herbage, as well as moss and fern have 

 formerly flourished ; and on the arid plains seedling trees may have 

 appeared again and again but only to perish in all the leaves of their 

 spring. And to the rainfall may be attributed the limitation as well 

 as the determination of the distribution of each. 



It has been intimated by a writer, quoted in the preceding section, 

 that much depends on the distribution of rain in time as well as in 

 space. 



From what has been advanced we may infer that of the seeds of 

 grasses, of herbs, and of trees alike, falling anywhere, like the mould 

 germs alighting on the cheese, the orange, and the pear, those only 

 which found there all the appropriate conditions of germination, growth 

 and reproduction would there flourish and be reproduced, and any 

 failure of the requisite conditions, occurring at any time, would 

 prove fatal to them. An appropriate supply of moisture is one of 

 those conditions. Under artificial culture we may see a plant damp 

 ofi", turnips braird but never come to maturity, and a seeding tree 

 perish from drought : thus may seedling trees have perished on the 

 plain, a consequence of the distribution of the rainfall, and in the 



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