THE ORIGIN OF PLANT-STRUCTURES. 379 



without the aid of Natural Selection," at once challenges a com- 

 parison with the well-known book of six-and-thirty years ago, not 

 altogether to the advantage of the present one. There is something 

 in the style which javs a little. It lacks the modesty of genius. If 

 Mr. Henslow will pardon the expression, he is too cocksure. 



As the Introduction is a statement of his case, it may be useful 

 to point out one or two weak places in his line of argument. For 

 instance, on p. 4, he would "strongly emphasize this fact," that 

 the natural selection from a number of seedlings is merely a matter 

 of "constitution"; the stronger survive, the weaker perish: it is 

 quite independent of any " structural differences " arising from 

 the law of variation. Mr. Henslow does not define "constitution," 

 but evidently admits its liability to an indefinite variation, which, 

 however, he quite refuses to accept in points of structure. " I would 

 ask," he says, " if there is any evidence, direct or indirect, that any 

 such trivial morphological differences .... are of the slightest 

 consequence to a seedling, so as to enable it to survive in the 

 struggle for life ? " We think there are. "Damping off" some- 

 times plays terrible havoc among seedlings. Is it not possible to 

 imagine that those which survive may do so on account of a shght 

 structural variation in the direction of a thicker cuticle more 

 resistant to the attack of the fungus spore ? Branching in the 

 axils of the cotyledons sometimes takes place. This is a morpho- 

 logical variation, and would be of great value in the struggle for 

 light and air, enabling the seedling in which it occurred to over- 

 shadow those on either side of it, or, in case of injury to the mala 

 shoot, to still continue growth. 



" A seedling survives among others solely because it is vigorous. 

 This is capable of proof," The proof given is that "larger and 

 better nourished 'seeds' have a much greater facility in starting, 

 and soon crowd upon the rest by growing more quickly into larger 

 plants." But this simply means that the indefinite variation which 

 obtains among the seeds of a capsule exercises an important 

 influence on the survival or death of the seedling. Variation in 

 "vigour" is probably a variation in the amount of endosperm 

 [i.e., in the size of the asexual plant-body, if we grant the some- 

 what doubtful relation between the endosperm of an angiosperm 

 and the fern prothallium), or the thickness of the seed-coat or some 

 other structural character. 



In support of his contention that morphological adaptations 

 arise " solely through the direct action of the new environment," 

 the author cites the manner of growth in desert plants, " dotted 

 about, never forming large masses." " There is absolutely no 

 struggle at all with each other ; but the struggle is all against 

 the physical difficulties of soil and climate." But this is not the 

 only conclusion possible. Does only one seedling come up for 

 each of the isolated adults ? Or are the fertile spots those which 

 are sufficiently favoured in some condition of soil or moisture or 

 shelter to make growth possible ? And is Mr. Henslow certain 

 that no struggle between individuals takes place on these little 

 oases ? 



