752 TRANSACTIONS OF SECTION K. 



4. Differentiation of Sex in Thallus, Gametophyte, and Sporophyte. 

 By A. F. Blakeslee, Ph.D. 



For the sake of discussion the germination of the zygospore of the Mucors 

 may be compared with the germination of the zygote of higher forms. The germ 

 tube of the Mucors would then be homologised with the sporophyte, and the 

 mycelium with the gametophyte. To avoid the confusion occasioned by the 

 terms ' monoecious ' and ' dioecious,' which are indiscriminately applied to both 

 generations, homothallic and heterothallic may be used in the gametophyte, and 

 homophytic and heterophytic in the sporophyte, to distinguish more precisely the 

 sexual condition in these stages. 



All Phanerogams are heterothallic : Lilium may represent the homophytic, and 

 Populus the heterophytic types. 



In the Pteridophytes, Polypodium may represent the homothallic forms. The 

 heterothallic forms may be represented by Selayinella, which is homophytic. No 

 heterophytic species are known to exist. 



Homo- and hetero-thallic forms occur among the Bryophytes, but up to the 

 present time the sexual condition of their sporophyte has not been investigated. 

 Evidence is at hand, however, which would indicate that the sporangium of 

 Marchantia polymorplia., like the germ sporangium of Phycomyces, contains both 

 male and female spores, and therefore this single species is to be classified as 

 homophytic. Attempts are being made with regeneration experiments to deter- 

 mine at what point in the development of the sporangium the segregation of sex 

 takes place. 



The Mucorinese, represented by Sporodinia, Phycomyces, and Mucor Mvcedo 

 respectively, constitute the only group in which the three possible types of 

 germination from the zygote are known. With the exception of the Mucors, the 

 sexual relations of the offspring from a single zygote in heterothallic Thallo- 

 phytes such as CEdoyonium, the zygotes of which give rise to more than a single 

 individual, have never been investigated. 



5. A Stigmaria of Unusual Type. By Professor F. E. Weiss, D.Sc. 



A Stigmaria of somewhat unusual type has been found in one of the nodules 

 from the Halifax Hard Bed of the Lower Coal Measures. It diifers from most 

 specimens of Stigmaria in the considerable amount of primary wood which was 

 centripetal in its development. In this character it resembles the Stiymaria 

 Brardi described by Renault.' The centripetal development of the primary wood 

 gives to the plant at first sight the appearance of a stem of Lepidodendron. But 

 Its stigmarian nature can be recognised by the absence of any hard outer cortex 

 ind by the characteristic periderm, to which are attached the remains of rootlet 

 cushions. The vascular tissue supplying these rootlets has practically the same 

 arrangement as that in Stiymaria Brardi of Autun, and the cortex has a con- 

 siderable development of short reticulated tracheids, the function of which is 

 still problematical. 



6. The Cross- Inoculation of Legutninosoi and other Root-Nodule hearing 

 Plants. By Professor W. B. Bottom ley. 



Nobbe, as a result of his researches, supposed that each leguminous plant 

 required its own specific organism for nodule formation. Frank considered that 

 each tribe of the Papilionacese had its specific organism. Beyerinck, whilst 

 describing at least two distinct tribes of these organisms, says the failure to pro- 

 duce inoculation upon all legumes with one bacterium is a diflference in variety 

 rather than in species. Quite recently Dr. Moore, of the U.S. Department of 

 Agriculture, has shown that it is possible to produce nodules upon practically all 



' Flore fosdle d' Autun. 



