1 the flowers on the same plant, or of the same kind of plant, they gave rise to forms like themselves, thus showing that they are true elementary species. It is also a point of some interest to observe that all these forms differed from each other in a large number of particulars. "Only one form, O. scintillans, that appeared eight times, is not constant as are the other species. When self-fertilized, its seeds pro FIG. 97. At left, section of chestnut, Castanea vesca, showing unusual variations; at right, a branch of Mercurialis annua, which presents several variations. (After de Vries.) duce always three other forms, O. scintillans, O. oblongata, and O. lamarckiana. It differs in this respect from all the other elementary species, which mutate not more than once in ten thousand individuals. From the seeds of one of the new forms, O. lævifolia, collected in the field, plants were reared, some of which were 0. lamarckiana, and others O. lævifolia. They were allowed to grow together, and their descendants gave rise to the same forms found in the lamarckiana 10. lata is always female, and cannot, therefore, be self-fertilized. When crossed with O. lamarckiana there is produced fifteen to twenty per cent of pure lata individuals. family, described above, namely, O. lata, elliptica, nannella, rubrinervis, and also two new species, O. spatulata and leptocarpa. V V V FIG. 98. Stamens of a hybrid willow, Salix auritax purpurea, showing different degrees of varying. "In the lata family, only female flowers are produced, and, therefore, in order to obtain seeds they were fertilized with pollen from other species. Here also appeared some of the new species, already mentioned, namely, albida, nannella, lata, oblongata, rubrinervis, and also two new species, elliptica and subovata. "De Vries also watched the field from which the original forms were obtained, and found there many of the new species that appeared under cultivation. These were found, however, only as weak young plants that rarely flowered. Five of the new forms were seen either in the Hilversam field, or else raised from seeds that had been collected there. These facts show that the new species are not due to cultivation, and that they arise year after year from the seeds of the parent form, O. lamarckiana.” FIG. 99.-A branch of a Japanese tree, Cryptomeria japonica, showing an atavistic variation. (After de Vries.) As to this we may observe: It has long been known that individual variations of an extreme degree sometimes occur, and that these may be to a degree persistent in heredity. Of such nature was the Ancon sheep, the Mauchamp sheep, the iceberg blackberry, and numerous other races or forms known in the domestication of animals, or the cultivation of plants. The generally normal structure of such individuals distinguishes FIG. 100.-A branch of the green Georgine, in which the inflorescence leaves and some of one branch (the right-hand one) are green like the rest of the plant, while the other varieties are red and in normal condition. (After de Vries.) them from monstrosities, which are usually freaks of development rather than of heredity. "' has The name "saltation," or in recent years "mutation," been applied to extreme fluctuation, the immediate cause of which is unknown. The experiments of de Vries on the saltations of the descendants of the evening primrose (called Enothera lamarckiana) have drawn general attention again to the possibility that saltation has had a large part in the process of The word mutation was first used not for saltations but for the slow fluctuation in successive geological periods. formation of species. As to this it may be said that the possible variation within each species is much greater than the range of the individuals which actually survive. The condition of domestication favors the development of extreme variation, because such individuals may be preserved from interbreeding with the mass, and they may survive even if their characters are unfavorable to competition in the struggle for existence. Among plants it is noticed that new soil and new conditions seem to favor large variation in the progeny, although the traits thus produced are not usually hereditary. Cases more or less analogous to those noted by Dr. de Vries are not rare in horticulture. The cross breeding of variant forms favors the appearance of new forms. Among actual species in a state of nature, there are very few which seem likely to have arisen by a sudden leap or mutation. The past and the future of de Vries' evening primroses are yet to be shown. The species called by de Vries Enothera lamarckiana is not at present known in its wild state anywhere in North America, the parent region of all the species of evening primroses or Enothera; so that we have as yet no reason to assume that the various mutants of the evening primrose are really comparable to the wild species of the same group now existing in America. While saltation remains as one of the probable sources of specific difference, the actual rôle of this process in nature is yet to be proved. CHAPTER X HEREDITY "Vom Vater hab' ich die Statur, Urahnherr war der Schönsten hold, Sind nun die Elemente nicht An dem Complex zu trennen; Was ist denn an dem ganzen Wicht Original zu nennen?" -GOETHE,"Zahme Xenien," vi. HEREDITY is the rule of persistence among organisms. The existence of such a law, or ascertained sequence of events," is a matter of common observation. "Like produces like," "Stature from father and the mood Stern views of life compelling; From mother, I take the joyous heart "Great-grandsire's passion was the fair. Great-grandam's, pomp and gold and show, And in my bones I feel it. "Of all the various elements That make up this complexity, What is there left when all is done, To call originality?" BAYARD TAYLOR's translation in part. |