262 NATURAL SCIENCE. Oct.. 



plants, I still maintain that " Mr. Henslow's theory [does not] utterly 

 break down." Mr. Wallace contends that the negative evidence 

 derived from "regular" flowers, as gentians, tells against me, as they 

 ought to have long ago become irregular, since their " lower petals 

 have been always subject to irritation and have never developed 

 irregular flowers." This is scarcely fair ; for not only do all botanists 

 believe — on precisely the same grounds of probabilities — that all 

 irregular flowers have descended (somehow) from regular ones; but 

 that, if he will refer to the chapter on " Peloria," he will see that 

 existing regular flowers, being mostly " terminal," have no " lower" 

 petals at all, but are so situated as to offer access to insects from all 

 points of the compass. Moreover, whenever a plant with normally 

 irregular flowers (which are always situated close to the axis, so that 

 insects can only enter them in one way) produces a blossom in a 

 terminal position (as foxglove, larkspur, horse-chestnut, etc., often 

 do), it at once becomes quite regular. These diff"erences between 

 regular and irregular flowers represent two of those groups of coinci- 

 dences respectively, to which I referred. 



Mr. Wallace adds : " The very first essential to this theory is 

 to prove that modifications produced by such irritations are 

 hereditary." Quite so. But this proves itself, if my contention be 

 right ; for plants with irregular flxowers are all hereditary. So that there 

 is no need to prove this point, provided the " previous question " as 

 to the origin of irregular flowers themselves be answered. But the 

 converse change can be readily shown ; for flowers, normally irregular 

 in nature, often revert to their ancestral regular form under cultivation 

 in the absence of insects, and then come true from seed, as do 

 Gloxinias. Unfortunately, one cannot make a regular flower become 

 irregular. How long it required in nature to do so no one can tell ; 

 but all the innumerable minute details of structure coincide to one 

 end ; a multitude of correlations all fit together for one effect ; so that 

 we may put the alternative thus — Which is more likely, that some 

 one common cause has set up these minute, often microscopic, details 

 in unison together ; or that they have arisen by selection out of 

 Innumerable wasted variations, which no one ever saw in nature, nor 

 can even ever see a trace of under cultivation ? 



When, however, we come to variations in the vegetative system 

 of plants, there is nothing easier than to prove, first, the direct action 

 of the environment, and secondly, the hereditary persistence of the 

 result. I need go no further than to take Buckman's parsnip, 

 Carriere's radish, Vilmorin's carrot, or anybody's variety of cabbage. 

 What are all these and many other instances but experimental 

 verifications. 



Mr. Wallace alludes to my last paper on " The Origin of Plant- 

 Structures by Self-Adaptation to the Environment, exemplified by 

 Desert and Xerophilous Plants, "'3 and attacks my inferences with 



^^ Journ. Linn. Soc. Bot„ xxx., p. 21S. 



