966 LIFE : OUTLINES OF GENERAL BIOLOGY 



usually regarded as the product of natural selection acting on 

 "spontaneous" local variations ; nor need its application be restricted 

 to the vegetable kingdom only. ^ 



LOCALISATION OF PLANT-RESERVES.— As such localisations 

 occur in very various situations in different plants, yet all get utilised 

 as required, particulars of these seem of little interest from the 

 physiological point of view; and even the morphologist has paid little 

 beyond descriptive attention to the characteristic forms they 

 assume, and thus practically left them within the vagueness of 

 "indefinite variations". But in some cases, at least, we can group 

 these in definite order; as notably among our most famiUar cruci- 

 ferous plants, like greens, cabbages, and turnips. For what more 

 natural than that leafage like that of our common greens and kale, 

 actively photosynthetic while also keeping on their growth, should 

 be understood as first of all utilising their abundant growth-material 

 in enlarging their own leaf-surface — and this most simply with 

 expansion of its marginal area, where least restrained by the harden- 

 ing of the woody element of the smallest fibro-vascular bundles 

 and the toughening of their bast elements — so giving us our famiUar 

 curly kale. Where the fibro-vascular network can yield more uni- 

 formly, the whole leaf can enlarge more simply too, as in our ordinary 

 cabbage; but if it early becomes more resistant, the growing leaf 

 parenchyma cannot but bulge upwards, even with more or less 

 wrinkling, as seen in varieties of the savoy cabbage; while in sea- 

 kale it is evidently the region of the mid-rib and leaf-stalk which 

 yields most readily to parenchymal growth and storage. As the 

 outer (i.e. basal) leaves of our common cabbage reach maturity, see 

 how they more and more contribute to the magnitude of the younger 

 apex-ward leaves, which they successively cover and enclose, so 

 producing the immense yet simple bud-form so characteristic of the 

 cabbage. A kindred, yet distinct phase and form appears when the 

 leaf -surplus goes to nourish, accelerate, and enlarge the leaf -buds, 

 as in Brussels sprouts; and yet a further when it is carried on into 

 the inflorescence, as in cauliflower. In Jersey cabbage the surplus 

 largely descends towards lengthening the stem, so there giving us 

 no appreciable store; but in the turnip the store is laid up abim- 

 dantly in the extending parenchyma at origin of stem and root, and 

 as reserve for biennial life with flowering and seeding; but which, 

 when appropriated by us at close of its first season's growth, has 

 yielded the most important revolution in stock-keeping since 

 the ancient invention of hay, since for cattle-keeping over winter 

 altogether the most profitable in history. The like transition in 

 utilisation of reserves leads from the exuberantly leafy artichoke 

 to its near garden ally, the midrib-succulent cardoon ; while in the 

 artichoke that enlargement and storing of reserves in the broadened 



