capable of producing like individuals by the ordinary 

 processes of reproduction," and with this Prof. Farlow 

 agrees in his statement that " A species is a perennial suc- 

 cession of like individuals." To some such definition as 

 this most students will subscribe, and it only remains for 

 us to decide what are the " like individuals " of Prof. 

 Farlow's definition, and what constitute the " essential 

 differences " mentioned by Prof. Underwood. 



Unfortunately, botanists at present are not disposed to 

 agree on these points, and Prof. Underwood has exactly 

 expressed the state of affairs by the statement that 

 " Sytematists seem inclined to make a species what they 

 choose." True species, however, are matters of fact and 

 not of opinion. It is a fundamental principle of evolu- 

 tion, though seldom admitted by radical botanists, that 

 all species vary to a certain extent ; indeed, it is now be- 

 lieved that the object of cross-fertilization in nature is 

 not the securing of stronger offspring, but the produc- 

 tion of variation. This being so, it is not to be expected 

 that any species can be marked out by hard and fast lines. 

 It is well known that many botanists are fond of saying 

 that a species is the smallest recognizable segregate, but 

 DeVries' work among the plants has shown that there 

 are many forms that are but temporary in nature, and 

 therefore not entitled to rank as species. We have only 

 to turn to the breeders of plants for illustrations of the 

 ultimate segregate theory. Xo botanist regards the gar- 

 dener's hundreds of different cabbages and squashes as 

 separate species, although they are distinguishable from 

 one another and come true from seed. Why then should 

 we give greater consideration to similar forms in na- 

 ture? If every variation in the cutting of a sterile leaf 

 in the genus Botrychium is sufficient to constitute a spe- 

 cies, why are not the variations of the lady fern (Athyr- 

 ium filix-fcemina) , many of which are extensive enough 

 to affect the shape and size of the whole frond, entitled 

 to the same consideration? 



The truth is, there are various degrees of resemblance 

 and therefore various degrees of difference. Some are 



