xiv AUTHORS' PREFACE 



While on this subject, we may be permitted to remark that the 

 constancy of a species is very remarkable and well deserves our 

 admiration, if we merely take into view the period of time over 

 which our investigations can extend with some degree of certainty. 

 We see, in fact, species brought into cultivation before history 

 began, exposed to all the modifying influences which attend seed- 

 sowing incessantly repeated, removal from one country to another, 

 the most important changes in the nature of the countries and 

 climates through which they pass, and yet these species preserve 

 their existence quite distinct. Although continually producing 

 new varieties, they never pass the boundaries which separate them 

 from the species which come next to them. 



Among the Gourds, for example, which are annual plants that 

 have been in cultivation from times so remote that assuredly many 

 thousand generations of them have succeeded one another under 

 the conditions which are best calculated to bring about important 

 modifications of character, we find, if we give ever so little attention 

 to the subject, the three species from which all the varieties of 

 cultivated edible Gourds have originated ; and neither the influences 

 of cultivation and climate, nor the crossings which may occur from 

 time to time, have brought forth any permanent type or even a 

 variety which does not speedily revert to one of the three primitive 

 species. In each of these species the number of varieties is almost 

 indefinite, but the limit of these varieties appears to be fixed. Does 

 any plant exhibit more numerous or more diversified varieties of 

 form than the cultivated Cabbage? Is any difference more marked 

 than that which exists between a Round-headed and a Turnip- 

 rooted Cabbage, between a Cauliflower and Brussels Sprouts, 

 between a Kohl-Rabi and a Tree Cabbage ? And yet these vast 

 dissimilarities in certain parts of the plants have not affected the 

 character of the essential parts of the plants, the organs of fructifi- 

 cation, so as to conceal or even to obscure the evident specific 

 identity of all these forms. While young, these Cabbages might 

 be taken for plants of different species, but when in flower and in 

 seed, they all show themselves to be forms of Brassica oleracea, L. 



It seems to us that the long-continued cultivation of a very 

 considerable number of kitchen- garden plants, while it demonstrates 

 the exceedingly great variability of vegetable forms, confirms the 

 belief in the permanence of those species that are contemporary 

 with Man, and leads us to consider each species as a kind of system 



