288 



SCIENCE. 



[N. S. Vol. I. No. 11. 



of the records of their origins, and because 

 such records of any varieties are few we 

 have come to overlook the fi-equency of 

 bud- variation and to ascribe all progressive 

 variability in the vegetable kingdom to 

 seeds or sex. 



Whilst it is not my purpose to discuss 

 the original sources of bud- variations, I 

 cannot foi'bear to touch upon one very re- 

 markable fact concerning reversions. It is 

 a common notion that all bud-varieties are 

 atavistic, but this position is untenable if 

 one accepts the hypothesis, which I have 

 here outlined, of the ontogenetic individual- 

 ity of the phyton, and if he holds, at the 

 same time, to the transforming influence of 

 environment. It is also held by some that 

 bud-varieties are the effects of previous 

 crossing, but this is controverted by Dar- 

 win in the statement that characters some- 

 times appear in bud-varieties which do not 

 pertain to any known living or extinct spe- 

 cies ; and the observations which I am 

 about to recite also indicate the improba- 

 bility of such influence in a lai'ge class of 

 cases. The instances to which I call your 

 attention are, I think, true reversions to 

 ancestral types. Those of you who have 

 observed the young non-blooming shoots of 

 tulip-tree, sassafras and some other trees 

 will have noticed that the leaves upon them 

 often assume unusual shapes. Thus the 

 leaves of sassafras often vary from the typ- 

 ical oval form to thi-ee-lobed and mitten- 

 shaped upon the strong shoots. There are 

 the most various forms on many tulip-trees, 

 the leaves ranging from almost circular and 

 merely emarginate to long-ovate and vari- 

 ously lobed ; all of them have been most 

 admirably illustrated and discussed recently 

 by Holm in the proceedings of the National 

 Museum. Holm considers the various 

 forms of these liriodendron leaves to be so 

 many proofs of the invalidity of the fossil 

 species which very closely resemble them. 

 This may be ti-ue, for there are probablj'' no 



specific names of organisms founded upon 

 so fragmentary and scant material as those 

 applied to fossil plants ; and yet I cannot 

 help feeling that some of these contempora- 

 neous variations are reversions to verj' old 

 types. I was first led to this opinion by a 

 study of the sports in ginkgo leaves, and 

 finding them suggestive of Mesozoic tj'pes. 

 " This variation in leaf characters," I wrote 

 at the time, " recalls the geologic liistorj' of 

 the ginkgo, for it appears to be true that 

 leaves upon the j'oung and vigorous shoots 

 of trees are more like their ancestors than 

 are the leaves upon old plants or less vigor- 

 ous shoots, as if there is some such genea- 

 logical record in leaves as there is in the de- 

 velopment of embryos in animals." Subse- 

 quent observation has strengthened my be- 

 lief in the atavistic origin of manj^ of these 

 abnormal forms, and this explanation of 

 them is exactlj^ in line with the characters 

 of reversions in animals and in cultivated 

 plants. It would, of course, be futile to at- 

 tempt any discussion of the merits of the 

 specific types proposed by palfeobotanists, 

 but in those cases, like the ginkgo, where 

 the geologic types are fairly well marked, 

 constant and frequent, and where the similar 

 contemporaneous variations are rare, there 

 is apparently good reason for regarding 

 contemporaneous forms as fitful recollec- 

 tions of an ancient state ; and this supposi- 

 tion finds additional sujiport in the ginkgo, 

 because the species is becoming extinct, a 

 fact which also applies to the tulip-ti-ee, 

 which is now much restricted in its disti'i- 

 bution. I am further reinforced in this view 

 by Ward's excellent study of the evolution 

 of the plane-tree, for, in this instance, it 

 seems to be well determined that the geo- 

 logic tj'pe has fau'lj^ well marked specific 

 characters, and the auricular or peltate base 

 upon contemporaneous leaves, which re- 

 cords the connection between the two, is 

 sufficiently rare to escape comment. Va- 

 rious waiters have remarked upon the 



