738 THE POPULAR SCIENCE MONTHLY. 



deeper down even than that, since both belong to the same colony 

 at the same period of failing growth, the impulse to fresh effort 

 afforded by such a union would appear to be less ; indeed, in some 

 cases it is quite inoperative ; whereas, when each comes from a 

 separate plant, not only are the chances of diversity in constitu- 

 tion greater, but the constitutional fillip or stimulus to growth is 

 more distinctly marked. Birth is a result of the union of unlike- 

 nesses. 



Hence, while among the lowest and least developed flowers 

 self-fertilization (or, to speak more correctly, fertilization of each 

 ovary by its brother-stamens) is very common, among the higher 

 and more specially adapted plants devices for promoting cross- 

 fertilization, either by wind or insects, are almost universal. In 

 some instances, indeed, the ovary can not be impregnated by pol- 

 len coming from the same flower — the fillip does not seem suffi- 

 cient to promote growth, and the ovary touched only with pollen 

 of a neighboring stamen remains to the end perfectly sterile. 

 Truly distinct pollen is needed to quicken it. In other cases, 

 though such incapacity does not exist, special arrangements have 

 been made to prevent self-fertilization — the stamens and pistils do 

 not mature together, or else they are so arranged in the blossom 

 that contact of the pollen with the stigma is almost impossible. 

 And in some of the very highest plants of all, the stamen-bearing 

 and ovary-bearing flowers are distributed on totally distinct trees 

 or bushes, thus affording the most perfect known development of 

 the sexual principle — a sort of automatic compulsory exogamy, 

 whereby each blossom must needs intermarry with a member of 

 an entirely different colony. 



For the same reason it will now, I hope, at once be clear why 

 the offspring in every case resembles on the whole both parents 

 equally. The various leaves which each rose-tree puts forth are 

 exactly alike, and we don^t expect them to be at all otherwise, 

 because they are all similar products of the self- same active and 

 formative energy. However much we may subdivide the parts of 

 a plant, we look forward to finding its manifestations remain un- 

 changed, as in the familiar case of cuttings, grafts, layers, suckers, 

 bulbs, and runners. The different leaves, made of the same ulti- 

 mate stuff, the new material of the species, resemble one another 

 exactly as two parts of the same lump of clay or putty have simi- 

 lar characters ; or exactly as the two halves of the same crystal re- 

 build their lost parts and renew their original shape alike when 

 immersed in a mass of the same mother-liquid. So, too, we may 

 well believe the undeveloped embryo or unfertilized seed poten- 

 tially resembles in all things (as far as it goes) the mother-plant ; 

 but, as soon as it is fertilized by the pollen from its neighbor, it 

 becomes in every portion of itself part and parcel of two previous 



