32 DR. SCIILEIDEN'S THEORY OF AGRICULTURE. 



after two or three more or less abortive efforts they completely 

 vanisli. 



As regards tlie second group, how different are the roots of our 

 cultivatetl Carrots, Turnips, «S;c., from tiie dry, useless produce 

 of the wild plant ! What resemblance between our CauliHowers, 

 Savoys, and Cabbages, and the juiceless plants of Brassica 

 oleracea from the Dunes of the Baltic, which, nevertheless, is 

 the origin from which they sprang ? The wild Potato of Chiloe 

 has a small, greenish, nauseously bitter root, and other instances 

 might be alleged. The characteristic, then, of agricultural 

 plants consists not in what distinguishes them as species, but in 

 that which separates them as varieties from the typical form. 



Moreover the natural orders to which they belong are amongst 

 those which have an especial tendency to form varieties, '\i\ 

 which, therefore, the distinction of species is extremely difficult, 

 and requires great circumspection. To understand then the 

 peculiarities of these plants we must become well acquainted 

 with the mode of origination of varieties and subspecies. If the 

 seeds of a double Dahlia are sown, a few only of the produce 

 resemble the parent, the greater part differ from that and from 

 each other ; and when the same circumstances take place in the 

 second generation the plant which exhibits them is called a 

 variety. The Cauliflower, for instance, was originally a variety 

 of the wild Cabbage. If proper attention, however, be paid to 

 the soil, the seeds reproduce the variety with certainty, and it is 

 then called a subspecies. 



But few varieties arise from mere cliange of soil or climate : the 

 flesh-coloured Hi/di-angea becomes blue in certain soils ; some 

 blue flowers become red when grown near anthills from the effect 

 of the formic acid ; and in a dry situation the lliband Grass of 

 our gardens is produced from the common green form. Changes 

 of colour and increase or decrease of vigour are effected, but new 

 varieties in general do not arise. 



Where plants are propagated by buds varieties more frequently 

 originate. Potatoes for instance alter more or less in different 

 soils, and Strawberries degenerate where they are allowed to 

 spread extensively from runners. 



The main source, however, of varieties and subspecies is from 

 seed. Art indeed exercises a certain degree of power over their 

 production, so that the expected produce is almost matter of cal- 

 culation where a sufficient degree of skill is exercised. If tiie seeds 

 of a variety are sown with due attention to similarity of soil and 

 treatment, there is almost a certainty that some individual will 

 exhibitHhe characters of the variety. If amongst these that one 

 is selected which is nearest to the mother-variety, the new gene- 

 ration will afford a greater number of individuals true to the 



