MONOGRAPH OF THE BRITISH SPECIES OF EUPHRASIA. 



327 



likeness to one or the other, or it may be different from either. 

 Or, two hybrids may originate a form which cannot be phiced in 

 the genas. As instances of species which are the result of hybridity 

 he gives the following: — FL Port<s ; E. Stiriaca; E. pulchella; E. 

 drosocaly.v (= /.'. capitulataJ Towns.). 



2. Varied Climatic Conditions. — The spreading of a species over 

 areas with different climatic conditions or climatic changes within 

 one and the same area may produce new forms or species. The fact 

 that species are very gradually changed by altered climatic influences, 

 and that new species are very slowly formed by them, throws great 

 light on the subject of species-building by these means. The 

 changes are brought about by a power which can further develop 

 or can degrade existing organs, but cannot create new ones. And 

 herein lies the great difference between the change caused by 

 hybridity and that caused by cHmate; in the latter case the change 

 is not brought about by an innate power in the plant itself, and only 

 fixed by altered climatic influences and environment, but the change 

 is virtually caused by these latter factors, and not by the selecting 

 power in the battle for existence. I believe I rightly interpret the 

 Professor's meaning to be that natural selection does not originate, 

 though it is a power in fixing, the new forms. 



3. The repeated and continued arrest of the growth of a 

 species will originate new forms. As an instance of change brought 

 about by this means, Prof. Wettstein refers especially to the relation 

 between E. mnntana and E. Bostkoviana. The ancestor of these 

 species was a summer-blooming one ; in long herbage the plant 

 could bloom with difficulty, being on the one hand smothered by 

 grass, on the other being cut down by the scythe ; hence only 

 abnormally early blooming plants or abnormally late blooming ones 

 could come to perfection and ripen seed. E. wontana is the repre- 

 sentative of the early, and E. Rostkoviana of the late-blooming forms. 

 E. tenuis and E. hrcvipila, E. carulea and E. carta, have a similar 

 relation to each other. Prof. Wettstein instances an analogous 

 case given by Wallace and termed by him Sidson diworphisums, 

 differing, however, in that the change here takes place in one 

 generation, whereas many generations have been required to pro- 

 duce the change in Euphrasia. Prof. Wettstein proposes the term 

 Saison-i/cneratiu)is dimorphis)iius for the former, and Saison-Artdi- 

 morphiswus for the latter. Prof. Wettstein does not definitely 

 allude to the influence of variety in soil, chemical or otherwise. 

 Remarkable instances are given of change induced by such influences 

 in Dr. Eugenius Warming's Lchrbnch der OckohMjischcn Pflanzen- 

 (jcoi/ rapine, page 63 (Germ, ed., 189G). Sadebeck, beginning in 1871, 

 cultivated Adiantum Serpentini and A. adulterinuin for sixteen genera- 

 tions, and tliese species reverted to A. Adiantum -ni(irum and A. viride. 



Though it may seem that tlie members of this polymorphous 

 genus are distributed without order, it must be remembered that 

 without doubt the earlier members were in the first instance fewer, 

 more closely related, and more distinctly grouped; but changes of 

 climate within the areas, and the extension of forms into areas with 



