DESIGN IN THE ORGANIC WORLD. 437 



moderate degree of heat, can manufacture their own food out of 

 the inorganic components of air and water \ and can thus flourish 

 at all ordinary temperatures, wherever they can get an adequate 

 supply of these elements. Most of the higher Plants, on the other 

 hand, whilst still capable of generating out of air and water the 

 organic materials which they require for their own sustenance, 

 need also to be supplied with certain special mineral substances ; 

 and will only flourish within certain limits of temperature. More- 

 over, as Mr. Darwin has shown us, many of them require the 

 agency of Insects for the fertilization of their ovules ; and cannot 

 reproduce themselves by seeds where that agency is not supplied. 

 But the aggregate of these physical conditions constitutes only a 

 part of the cause of the Plant's growth : there must be an aptitude 

 on the part of the organism itself to turn them to account ; and of 

 the source of that aptitude, we at present know nothing whatever. 

 Some Plants can adapt themselves in a much greater degree than 

 others, to differences in external conditions; that adaptation 

 involving some modification of their own structure. " What," 

 said Professor Lindley, fifty years ago, " is a ' common ' plant, but 

 " one which can grow and propagate itself in almost any kind of 

 " soil, and under almost every range of temperature ; and what is 

 " a 'rare' plant, but one which cannot flourish and produce seed, 

 " except under certain special conditions ? " Every botanist 

 knows that among our own wild plants, Rosa, Riibus, and Salix 

 are alike the most "variable," and the most "common" types; 

 " common," because they have the capacity for adapting them- 

 selves to different conditions of growth ; " variable," because of 

 the influence of those varying conditions upon their organization. 

 Out of the forms of Rose, Bramble, and Willow, ranked as 

 " varietal " by Mr. Bentham, our ablest student of them, previous 

 systematists had created more than three hundred "species." 



Take, again, the influence of cultivation. There is no more 

 remarkable example of the alteration produced by more abundant 

 supply of food and more regulated temperature, than that ex- 

 hibited in the development of the wild Brassica okracea, a rambling 

 sea-shore plant, into the various kinds of cabbage, broccoli, and 

 cauliflower. Why will not culture produce the like effect upon 

 other plants ? It is (juile illogical to say that this transformation 



