December 26, 1913] 



SCIENCE 



933 



was further observed that even in the ease of 

 the functional mother cells, that the tetrads 

 frequently produced but one normal pollen 

 grain, the other three persisting as mere 

 vestiges, attached to the germination pores of 

 the completely formed grains. In normal 

 B. pumila abnormalities of this nature were 

 not found. Another interesting feature of the 

 development of the microsporangium in the 

 material from the Arnold Arboretum was the 

 abortion of the mechanical or fibroid layer of 

 the anther wall, which in normally developed 

 spore sacks is responsible for the dehiscence 

 of the anthers. Both these features of the 

 stamens of the specimens under discussion, 

 viz., the abortive pollen and the degenerate 

 anther wall, point unmistakably to their hy- 

 brid origin. 



Professor Jack has been good enough to 

 supply the history of the plants of B. pumila, 

 growing in the Arnold Arboretum. They were 

 derived from seed obtained from plants pro- 

 pagated at the Arboretum from wild seed of 

 the species, secured by Professor Sargent m 

 Vermont. A few of the group of individuals 

 thus obtained were clearly hybrids between 

 B. pumila and near growing large trees of B. 

 lenta. The peculiarities of ray-structure re- 

 ferred to above, namely the aggregation phe- 

 nomena, are found in neither B. pumila nor B. 

 lenta, and are doubtless the result of the in- 

 creased vigor of heterozygosis, as has been 

 noted by Professor East and others. It ap- 

 pears quite obvious, from the various data 

 described here, that the plants of B. pumila 

 at the Arboretum, although resembling that 

 species absolutely in external form, are in 

 reality hybrids, as inferred from their more 

 important anatomical features. 



The next illustration of the value of ana- 

 tomical data in the diagnosis of hybrids is 

 taken from the genus Equiseium. The species 

 of this genus known as E. littorale has long 

 been recognized in Europe and this continent 

 as a hybrid between E. arvense and E. 

 limosum. It presents transitional features in 

 its external form and internal anatomy be- 

 tween these two species and moreover is char- 

 acterized by the production of large numbers 



of abortive spores, which are generally without 

 the " elaters " attached to normal Equiseium 

 spores. The genus Equiseium is character- 

 ized both in this continent and in Europe by 

 the large number of varieties of its species, 

 which occur spontaneously (these would prob- 

 ably be designated by mutationists of the De 

 Vriesian school as "elementary species"). 

 One of these numerous varieties is here taken 

 as an illustration of the value of anatomy in 

 genetical work. Professor Jeffrey observed in 

 material of B. variegaium var. Jesupi, gathered 

 on Toronto island, that a large number of the 

 spores were abortive and without elaters. A 

 detailed anatomical investigation of this mate- 

 rial and of other specimens, including the 

 type, kindly supplied for this purpose by the 

 Gray Herbarium of Harvard University, 

 showed that not only are the spores largely 

 abortive in E. variegaium var. Jesupi, but 

 that the sporangium wall is also degenerate, 

 lacking the mechanical or fibrous layer. The 

 aerial and subterranean stem further showed 

 a condition of organization intermediate be- 

 tween that found in E. hiemale and E. varie- 

 gaium. E. variegaium var. Jesupi, is conse- 

 quently not to be regarded at all as a variety 

 or " elementary species," but as a clear hybrid, 

 in all probability between E. hiemale and E. 

 variegaium. The writer hopes later to pub- 

 lish extended observations on a number of the 

 " varieties " of species of Equiseium. 



In conclusion it may be pointed out that 

 the investigation of the anatomy of recognized 

 or crypthybrids is likely to be of great value 

 from the genetical standpoint and wiU in all 

 probability lay bare the real foundation in fact 

 of the so-called mutation hypothesis of De 

 Vries. 



E. HOLDEN 



Laboratories op Plant Moepholooy, 

 Habvakd University 



THE OEIO ACADEMY OF SCIENCE 

 The twenty-third annual meeting of the Ohio 

 Academy of Science was held at Oberlm College, 

 Oberlin, Ohio, on November 27, 28 and 29, under 

 the presidency of Professor L. B. Walton, of 

 Kenyon College. 



