198 SUMMARY OF CURRENT RESEARCHES RELATING TO 



passage of the rhizome undergrouud. The aerial and subterranean 

 shoots are not absolutely fixed in the rudimentary stage, but are capable 

 of conversion one into the other (in Equisetum Umosuni). 2. The 

 rhizome, transversely geotropic, becomes under the influence of light 

 positively geotropic. 3. In species with variable leaf -number {E. arvense) 

 a reduction of the leaf -rudiments in acropetal succession can be brought 

 about by appropriate methods of culture (malnutrition in weak light). 

 4. Curvatures promote the outgrowth of side-shoots, the more they 

 afford to the latter a direct chance of negatively geotropic growth. 

 Other influences are light, moisture, etc. 5. Secondary increase in 

 thickness does not occur in Equisetum ; annual shoots can be made to 

 survive the winter. 6. Bower's view, that part of the spore-mother- 

 cell degenerates in the sporangia and serves for the nourishment of the 

 rest, is incorrect ; it is the periplasmodium, arising from the tapetum, 

 that serves for the nutrition of the spore-mother-cells. 7. In the 

 dehiscence of the antheridia the cover-cells take an active part and 

 curve open, recalling what happens in a moss-antheridium. 8. On pro- 

 thallia of some species {E. palustre, E. Schaffneri) tubers can be formed, 

 and can serve to luidge over times of mahnitrition, or to carry out 

 vegetative reproduction. 9. Fertile stems of E. arvense and J5'. Tehnateia 

 can by cultivation be made to turn green, and to put out side-shoots. 

 10. Capacity for regeneration differs in the different species. In general, 

 the future development of the shoots is already fixed in the rudimentary 

 stage ; E. limosum is an exception. 11. In the prothallia also there is a 

 strong capacity for regeneration. A meristematic tissue is formed, from 

 which new prothalHa are produced ; these become detached and inde- 

 pendent. 12. The sex of the prothallia is not definitely fixed ; male 

 may become converted into female, and vice versa. 



Leaves of Calamites.* — H. H. Thomas has studied the leaves of 

 Gahimites with a view to obtaining from their structure some indication 

 of the environment in which they grew. The material came from the 

 Lower Coal Measures (Halifax Hard Bed), and yielded five types of 

 leaf. The stelar structure of the leaf-bearing twigs proved to be inter- 

 esting. They appear to have grown in pendulous fashion, and the 

 structure of the mesophyll and epidermis suggests that the liabitat was 

 a damp one. The leaves possess some xeromorphic features. 



Fructifications of Jurassic Fern-leaves. f — T. G. Halle wTites on 

 the fructifications of Jurassic fern-leaves of the Cladophlehis denticidata 

 type. Some specimens preserved at Stockholm and at Cambridge appear 

 to be identical, and are referred by Halle to a new genus Cladotheca, the 

 species being C. undans, a synonym of which is Pecopteris undans Lindb. 

 and Hutt. Halle gives an account of the sporangia, with figures obtained 

 by moistening the surface of the fossils with cedar-oil, and then making 

 enlarged photographs. The sporangial structure recalls that of Senften- 

 hergia Corda, a palgeozoic genus which has been referred to Schizgeacea3, 

 to Marattiacese, and to Primofilices. In an addendum Halle says 

 Gladotheca is nearly related to I'odites Williamsoni. 



* Phil. Trans. Roy. Soc, B, ccii. (1911) pp. 51-92 (3 pis.), 

 t Arkiv for Bot., x. (1911) No. 15, 10 pp. (2 pis. and fig.). 



