September 30, 1892.] 



SCIENCE. 



This geological proof seems to me to be absolutely incontro- 

 vertible, and reduces to nil hypotheses built on the apocryphal 

 documents left by an adventurer like Sebastian Cabot, the inac 

 curacies of which, not to say the fancies, are shown by the exam- 

 ples we have cited. 



The true horse (Equus) has been scattered more widely, and 

 has given rise to more species in North America than South 

 America. It is interesting to recall here that the remains of 

 Equus cdballus have been discovered in the Quaternary beds 

 (Pleistocene) of Canada and of Alaska. It is therefore certain that 

 this species has existed in the wild state in the American Arctic 

 region. But it is not less certain, according to all historical docu- 

 ments, that this animal had not existed for ages when it was in- 

 troduced by Europeans in the early part of the 16th century. 

 What is the cause which brought about the extinction of horses 

 in North America as in South America before thecommencement 

 of the present period ? This is not the place to discuss that ques- 

 tion. But I cannot refrain from remarking that the extinction ap- 

 pears to have coincided with that of the Proboscidians (Elephant, 

 Mastodon) and can consequently be attributed to the same causes 

 which are to be sought in the enviromnent of these Herbivorm 

 (nourishment, nature of the soil, etc.) 



For the present it will su93ce to establish that the Mastodon 

 superbus was contemporaneous with the Equus reetidens in the 

 in the Quaternary (Pleistocene) of the Argentine Republic. Also 

 Elephas primigenius is found with Equus caballus in the same age 

 in North America. All these types of animals became extinct in 

 the New World, although horses and elephants have continued to 

 live in Asia and in Africa up to the present time. 



ADAPTATION OF SEEDS TO FACILITATE GERMINATION. 



BY W. W. ROWLEE, COKNELL UNIVEBSITY, ITHACA, N.T. 



The observations recorded in these notes are based upon the 

 general law of evolution, that organisms are constantly adapting 

 themselves to secure advantages in their struggle for existence; 

 and, because of this, it is to be expected that all modifications 

 of organisms have some explanation in the economy of their ex- 

 istence. 



From the initiation of the young plant into life at the time of 

 fertilization of the ovule, to the end of the life of the mature 

 plant, there is no more critical period in its existence than when 

 it is dormant in the mature seed. It may be said in objection to 

 this statement, that such seeds as corn, wheat, and garden seeds 

 in general, when planted, almost all germinate, and this is true; 

 but these seeds are removed by artificial intervention from the 

 competition with which those planted naturally are compelled to 

 struggle. These seeds, then, may be left out of consideration. 



Careful observation of the seeds of native plants shows that a 

 very lai-ge percentage of them never germinate. Some, no doubt, 

 were never fertilized. I have counted a thousand seeds of different 

 species of plants belonging to the Order Composita;, and then planted 

 them carefully, giving them as good, if not better, conditions for 

 germination than they would have had if they had been planted 

 natui-ally, with the result that in most of the species a compara- 

 tively small number germinated. Anyone who will take the 

 trouble to search for seedlings of our native perennial plants, and 

 compare the number they find with the number of seeds produced 

 by the plant, will be convinced without further argument that the 

 larger proportion of seeds produced by wild planes never germinate 

 at all. In view of the critical period in the life of the plant when ' 

 it is dormant in the seed as an embryo, and recognizing the evo- 

 lutionary law of the survival of the fittest, is it not reasonable to 

 expect that modifications of the seed will be developed which will 

 facilitate germination? What are some of the modifications 

 which increase the chances for germination of the seed? 



In general, it may be said that seeds vary as to the structure of 

 the parts within the coats, as well as to the external appendages 

 of the outer coat. The internal characters are concerned with 

 the embryo and the albumen. The embryo is the essential part of 

 the seed. It consists of an initial stem, the bypocotyl, at each 

 end of which is a growing point, one, the plumule, destined to pro- 



duce the stem, the other, always at the other end of the bypocotyl 

 (usually termed the lower end), from which the primary root 

 starts. At the upper end of the bypocotyl, but below the plumule, 

 are the cotyledons, sometimes large, sometimes small. Surround- 

 ing the embryo more or less, and inside the coats, is the material 

 upon which the embryo is nourished until it can carry on an in- 

 dependent existence. This is termed the albumen of the seed. 

 Around all are the seed-coats. 



Moisture is as necessary to the germination of a seed as any 

 other external condition. The necessity for moisture would make 

 it highly probable that seeds should have special modifications to 

 secure it to the seed. It is my purpose to point out some of the 

 adaptations which seem to me to be designed to increase the facil- 

 ity and certainty of germination by securing and likewise keeping 

 constant the supply of moisture for the seed. Some of the char- 

 acters which will be mentioned have been considered as aiding 

 the seed in its distribution. These are flattened or feathered ap- 

 pendages commonly known as pappus, coma, etc. It is not my 

 purpose to belittle the office of distribution as performed by these 

 organs, but it does seem to me true that, while these organs do 

 assist the seed in dissemination, they, at the same time, aid in 

 bringing it into the most advantageous position for germination. 

 This advantage is often gained by the correlation of the internal 

 parts of the seed, especially the growing points, to the external 

 appendages of the seed or fruit. It is frequently the case that 

 there is but one seed in the ovary, and the coats of the ovary 

 closely invest the .seed. Such a fruit is an akene. If the ovary- 

 and seed-coats are completely fused together, the fruit is a cary- 

 opsis. For the purposes of our study these fruits may be included 

 in the same category with seeds proper. 



The correlation of parts in the seeds of many species is very 

 striking. In the akenes of most of the species of the Order Com- 

 positse it is especially noteworthy, and in several other orders 

 seeds occur showing the same correlation. They might well be 

 likened to an arrow. The feathered end is light, the head is 

 heavy. In falling, the heavy part, i.e., the part which contains 

 the embryo, is brought by the force of gravity invariably into 

 close contact with the soil. 



The same correlation of parts may been seen in the winged fruit 

 of any species of maple. There is a very fruitful silver-leaved 

 maple (A. dasycarpum) near my study. Under it passes a hard 

 gravel path. The fruits that fell in the smooth path, of comrse, 

 fell over on their side. Those that fell in the grass of the lawn, 

 almost invariably assumed a position with the wing up and the 

 body of the fruit down in the grass and leaves in contact with 

 the moist soil. Further, I found that not a single seed in the 

 path had germinated, when many of those in the grass had done 

 so. It was interesting to see those large seeds all wing-up in the 

 grass. 



Most of the fruits of plants belonging to the Order Compositae 

 are especially adapted to facilitate germination. As is well known, 

 the fruit is crowned with a pappus, which in a majority of cases 

 not only acts like a parachute and bears the seed away, but at the 

 same time lands it always a certain end up. The hypocotvl is 

 very short in proportion to the length of the cotyledons, and is 

 always in the lower end of the seed. Thus the growing points 

 are brought into close and constant contact with the moisture of 

 the soil. I have observed these akenes in fields and woods lodged 

 usually, I might safely say, almost always, in such a position as 

 to bring the akene with its lower tip in contact with the soil. 

 If it fell in an open, smooth place, it would tip over, but, although 

 reclining, would still have the lower tip upon the ground. If it 

 fell among grass, leaves, or debris of any sort, as seeds are very 

 apt to do, these would keep it in an upright position, and, on ac- 

 count of the barbed or upwardly roughened nature of many forms 

 of pappus, it would work its way down until it came in contact 

 with a suitable place for germination. 



To determine whether this could be proven experimentally or 

 not, I carefully selected a certain number of seeds of twenty dif- 

 ferent species, and planted one half of them one end up, the other 

 half with the other end up. I had grave doubts about the success 

 of the experiment, and should not have considered the proposition 

 improbable had no differences in the rate of germination afipeared. 



