694 EEPOBT— 1888. 



persistence of the germ-plasm. Yet it seems Lard to believe that the germ-plasm, 

 •while enshrined in the individual whose race it is to perpetuate, and nourished at 

 its expense, can be wholly indifferent to all its fortunes. It may be so, but in that 

 case it would be very unlike other living elements of organised beings. 



I am bound, however, to confess that I am not wholly satisfied with the data 

 for the discussion of this question which practical horticulture supplies. That the 

 contents of our gardens do exhibit the results of variation in a most astonishing 

 degree no one will dispute. But for scientific purposes any exact account of the 

 treatment under which these variations have occurred is unfortunately usually 

 wanting. A great deal of the most striking variation is undoubtedly due to wide 

 crossing, and these cases must, of course, be eliminated when the object is to test 

 the independent variation of the germ-plasm. Ilofi'mann, whose experiments I 

 have already referred to, doubts whether plants do as a matter of fact vary more 

 tmder cidtivation than in their native home and under natural conditions. It 

 would be very interesting if this could be tested by the concerted efi'orts of two 

 cultivators, say, for example, in Egypt and in England. Let some annual plant be 

 selected, native of the former country, and let its seed be transmitted to the latter. 

 Then let each cultivator select any variations that arise in regard to some given 

 character ; set to work, in fact, exactly as any gardener would who wanted to 

 ' improve ' the plant, but on a preconcerted plan. A comparison of the success 

 which each obtained would be a measure of the effect of the change of the environ- 

 ment on variability. If it proved that, as Hoffmann supposed, the change of con- 

 ditions did not affect 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 indivi- 

 duals. 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 find my mind somewhat shaken about it. Yet I feel disposed to say with 

 Mr. Darwin, ' I still imist believe that changed conditions give the impulse to 

 variability, but that they act in most cases in a very indirect manner.' 



Whatever conclusions we arrive at on these points, everyone 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 affinity, or the geographical distribution of 

 a plant may aflbrd, the living plant in itself is even more interesting stiU. 



Every organ will bear interrogation to trace the meaning and origin of its form 

 and the part it plays 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 investigations. But the field is well-nigh inexhaustible. The 

 extraordinary variety 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 morpho- 

 logical or physiological ne.riis varies, the rest will vary correlatively. One variation 

 then may, if advantageous, become adaptive, while the rest will be indifferent. But 

 it appears to me that such a principle 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 impression is that they will be found to be adaptive in innu- 

 merable 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 example, could possibly have guessed by inspection the pur- 

 pose of the glandular bodies on the leaves of Acacia sphm-ocephala and on the pul- 

 Tinus of Cecropiapeltata which Belt in the one case, and Fritz Miiller in the other have 



