BOTANICAL BIOLOGY. 411 



A comparison of the success which each obtained wouhl be a measure 

 of the effect of the change of the environment on variability. If it 

 proved that as Hoffmann supposed, the change of conditions did not 

 affect the what we may call the rate of variation, then, as Mr. Darwin 

 remarks in writing to Professor Semper, "the astonishing variations of 

 almost all cultivated plants must be due to selection and breeding from 

 the varying individuals. This idea," he continues, " crossed my mind 

 many years ago, but I was afraid to publish it, as I thought that people 

 would say, ' How he does exaggerate the importance of selection.' " 

 From an independent consideration of the subject I also lind my mind 

 somewhat shaken about it. Yet I feel disposed to say with Mr. Darwin, 

 "I still nmsf believe that changed conditions give the impulse to varia- 

 bility, but that they act in most cases in a very different manner." 



Whatever conclusions we arrive at on these points, every one will 

 agree that one result of the Darwinian theory has been to give a great 

 impulse to the study of organisms, if I may say so, as " going concerns." 

 Interesting as are the problems which the structure, the functions, the 

 aflfiuity, or the geographical distribution of a plant may aflbrd, the living 

 plant in itself is even more interesting still. 



Every organ will bear interrogation to trace the meaning and origin 

 of its form and the part it pla^^s in the plant's economy. That there is 

 here an immense field for investigation there can be no doubt. Mr. 

 Darwin himself set us the example in a series of masterly investiga- 

 tions. But the field is well-nigh inexhaustible. The extraordinary va- 

 riety of form which plants exhibit has led to the notion that much of it 

 may have arisen from indifferent variation. No doubt, as Mr. Darwin 

 has pointed out, when one of a group of structures held together by 

 some morphological or physiological nexus varies, the rest will vary 

 correlatively. One variation then may, if advantageous, become adapt- 

 ive, while the rest will be indifferent. But it appears to me that such a 

 ])rinciple should be applied with the greatest caution ; and from what I 

 have myself heard fall from Mr. Darwin, I am led to believe that in 

 the later years of his life he was disposed to think that every detail of 

 plant structure had some adaptive significance, if only the clue could 

 be found to it. As regards the forms of flowers, an enormous body of 

 information has been collected, but the vegetative organs have not 

 yielded their secret to anything like the same extent. My own impres- 

 sion is that they will be found to be adaptive in innumerable ways which 

 at present are not even suspected. At Kew we have probably a larger 

 number of species assembled together than are to be found anywhere 

 on the earth's surface. Here then is ample material for observation 

 and comparison. But the adaptive significance will doubtless often be 

 found by no means to lie on the surface. Who, for examjjle, could pos- 

 sibly have guessed by inspection the purpose of the glandular bodies 

 on the leaves o^ Acacia spharocephahi and on the pulvinus of Ccct-ojna 

 peltata which Belt in the one case and Fritz MUller in the other have 



