604 SUMMARY OF CURRENT RESEARCHES RELATING TO 



multiplying themselves indefinitely by asexual methods. The question 

 remained, whether the gametes of this hermaphrodite form, obtained 

 from a strictly dioicous species, could form an egg and therefrom a tetra- 

 haploidic sporogonium. But the Marchals, in testing this question, 

 found that their cultures of diploidic gonophytes, though kept under 

 observation for two years, remained completely sterile ; and yet an histo- 

 logical study of the sexual organs revealed no abnormality, save that the 

 antherozoids are rarely mobile. The Marchals accordingly concluded 

 that in the case of dioicous mosses the aposporic gonophytes are cursed 

 with an absolute sterility ; but that they can transmit their bisexual ity 

 to new individuals by vegetative propagation. This conclusion Cardot 

 regards as rather premature and as too absolute ; for he holds that in 

 certain unknown unexpected and unusual conditions the aposporic gono- 

 phytes might conceivably be provoked into a state of fertility ; and that 

 a diploidic aposporic race after a prolonged period of sterility might 

 become for a brief time fertile. Perhaps it would be wise to continue 

 the cultures for a long period of years. The Marchals have also studied 

 the behaviour of monoicous species (Amblystegium serpens, A. subtile, 

 Barbula muralis). The aposporic gonophytes obtained from them have 

 the same sexuality as normal gonophytes ; but the remarkable thing is 

 that diploidic state in no way hinders their fecundation. The resulting 

 sporophytes, when examined cytologically, were found to be tetraploidic, 

 the chromosomes showing themselves during the phases of sporogenesis 

 to be twice as many as in normal sporophytes and the chromatic elements 

 united in pairs. From the tetraploidic capsule are produced diploidic 

 spores, which are fertile and which fix definitely the new race, the bivalent 

 race. Finally, by regeneration from the tetraploidic sporophytes, some 

 tetraploidic gonophytes have been obtained, constituting a tetravalent 

 race, but have not yet been found to be fertile, the lapse of time being 

 insufficient. An interesting fact which results from the Marchals' cyto- 

 logical observations is that the size of the cells and of the nuclei is 

 distinctly larger in diploidic gonophytes than in normal gonophytes, and 

 is larger still in tetraploidic gonophytes. There is in fact a direct pro- 

 portion between the number of the chromosomes and the size of the 

 nucleus and cell. And correspondingly the reproductive organs them- 

 selves are of larger size. Consequently it is possible to find in the size 

 of the cells and nuclei (of, for example, the perigonial bracts, anthe- 

 ridia, spore-mother-cells, etc.) a criterion for the discrimination between 

 normal plants and the products of apospory. And in conclusion, some 

 simple experiments made by the Marchals show that young sporogonia, 

 when wounded, readily give rise to an aposporic protonema. Hence it 

 behoves bryologists to bear in mind the possibility of apospory when 

 studying the variability of mosses and the relations of allied species. 



Discoid Gemma? in Foliose Hepatics.* — N. E. Stevens gives an 

 account of the discoid gemmae in the leafy hepatics of New England. 

 In the leafy hepatics there are two distinct types of gemma?. 1. Those 

 of the simpler type are unicellular or bicellular, and arise in clusters on 

 leaf or stem near the apex. 2. Those of the second type are discoid 

 multicellular bodies, borne either on margin or surface of leaf. Gemmae- 



* Bull. Torrey Bot. Club, xxxvii. (1<J10) pp. 365-73 (figs.). 



