Maech 15, 1907] 



SCIENCE 



425 



As it is, the floating phase of Biccia lute- 

 scens has always been identified with R. na- 

 ians and is probably always labeled so in 

 collections. Which species is really B. natans 

 can probably only be told by examination of 

 the type specimens. Indeed, it is likely that 

 there are many more specimens of the floating 

 phase of B. lutescens labeled B. natans than 

 there are of the real B. natans^ as the former 

 is a much more conspicuous plant, and the 

 latter is for various reasons much more readily 

 overlooked. There are two distinct species in 

 question, and each has two distinct phases. 



The following brief diagnosis is, therefore, 

 appended : 



Biccia lutescens Schw., floating phase. 



Thallus bright green, usually semi-orbicular 

 to orbicular, its approximation to a complete 

 circle being dependent on presence or absence 

 of agitations of water-surface, waves tending 

 to separate thalli into segments. Upper sur- 

 face deeply furrowed, the main furrow func- 

 tioning as the dividing line of thalli in vege- 

 tative reproduction. 



Differing from R. natans, floating phase, in 

 larger size, brighter green color, relatively less 

 fully developed balancing scales, and from the 

 fact that it is conflned exclusively to tempo- 

 rary waters, while B. natans is found only in 

 permanent waters. 



Dr. W. H. Dall read ' Notes on Some Cre- 

 taceous Volutidae,' describing the development 

 from the Turonian upward of a group of Volu- 

 tidse which seems to have been derived from 

 some type like Piestochilus Meek, to have at- 

 tained a large size and striking characteristics 

 and to have culminated in the upper Senonian 

 or Eipley horizon in various parts of the 

 world. The group is found represented in 

 India, the Tyrol, North Germany and various 

 parts of North America, represented in each 

 region by analogous types, while each regional 

 group lias a certain local facies of its own. 

 In North America two lines of descent were 

 noted, represented by the genera Voluioderma 

 and Volutomorpha, neither of which is repre- 

 sented in any horizon subsequent to the Eip- 

 ley, though a distinct genus appears in the 



Tertiary of northwest America which has been 

 more or less confused with them. 



Dr. 0. F. Cook read a paper on ' Partheno- 

 genesis and Alternation of Generations in the 

 Parasitic Hymenoptera.' The discoveries re- 

 garding the embryology of the parasitic hy- 

 menoptera presented by Dr. Howard at a 

 former meeting of the society^ are not merely 

 a contribution to the study of sex-determina- 

 tion. They have brought to light an entirely 

 new form of alternation of generations among 

 the insects. Polyembryony is a botanical 

 term which fits these zoological facts but poor- 

 ly, and conceals a very close analogy with the 

 typical and original instance of alternation 

 of generations, that of the tunicates, described 

 by Chamisso in 1819. 



Polyembryony is the production or inclusion 

 of two or more embryos in one set of seed- 

 coats, instead of the usually single embryo. 

 But it does not follow that the multiple em- 

 bryos of plants are produced by vegetative 

 propagation of the original egg or embryo, as 

 are the chains of larvse in tunicates and in 

 these parasitic hymenoptera. Nor does the 

 body of the host in which these chains of in- 

 sect larvse are formed correspond to the em- 

 bryo-sac and seed-coats which enclose the mul- 

 tiple embryos of plants. The multiple plant 

 embryos arise, as far as known, from the pres- 

 ence of two or more ova in the embryo-sacs, 

 or from the intrusion of buds from the nu- 

 cellar tissue. The polyembryony of plants 

 has no necessary relation to sex-determina- 

 tion, for bisexual or hermaphrodite plants are 

 reproduced from multiple embryos. To mul- 

 tiply sexually differentiated plants by vegeta- 

 tive propagation does not affect their sexual 

 status, and the indications are that this is true 

 also of animals. 



Alternation of generations, that is, the al- 

 ternation between vegetative propagation and 

 sexual reproduction, has long been known 

 among the hymenoptera. The form of alter- 

 nation recently discovered in the parasitic 

 families differs from the other in that the 

 vegetative propagation takes place at a dif- 

 ferent period in the life history, in the early 



'Science, December 21, 1906, 810, 'Polyembry- 

 ony and the Fixing of Sex.' 



