78 SUMMAHY OF CURRENT RESEARCHES RELATING TO 



former abnormal condition has never yet been recorded, and indeed any 

 increase in the number of tetrads is rare. 2. Kantschieder's statement, 

 that in S. spinulosa only one macrospore mother-cell divides, while the 

 sterile sister-cells gradually become disorganized, is accepted also for S. 

 helvetica. But other writers, notably Campbell, dispute this ; and the 

 author has found in several instances two spore mother-cells in one 

 macrosporangium in the act of forming tetrads. 8. These cases of 

 abnormal spore-formation are regarded as atavism, and point to homo- 

 logies in the development of male and female organs. 4. Macrospor- 

 angia show a greater need of food-material than microsporangia ; 

 comparatively few macrospores are found on weak side-shoots : sometimes 

 indeed, there are only microsporangia. 5. A case of reduction to three 

 macrospores was observed in S. helvetica. 6. Dichotomous branching 

 at the apex of the sporangial branch is not rare in S. helvetica. 



Stock of Isoetes.* — W. H. Lang confirms H. von Mohl's view that 

 the roots of Isoetes are borne in regular order on a downwardly growing 

 region. This region is distinct and is not due to secondary modification 

 of the base of the leaf-bearing portion of the stele. The axis of Isoetes 

 can be compared with that of Lepidodendron and Pleuromeia, the root- 

 bearing region being strictly comparable with the stigmarian base of 

 these plants. 



Fossil Prothalli.t — R. C. McLean gives an account of two fossil 

 prothalli from the lower Coal Measures ; (1) in the pteridospermic seed 

 Lagenostoma Lomaxii ; (2; in the megaspore of the Lycopod Bothro- 

 dendron. The former specimen was found by J. Lomax, at Dulesgate, 

 and the description shows tbat the structure of the prothallus resembles 

 that of recent Gymnosperms, and probably originated by centripetal 

 alveolation. The other prothallus, Bothrodendron, probably came from 

 Dulesgate also. It is compared with Lepidostrobus Veltheimia?nis, 3Iazo- 

 carpo?i, 8alvinia^ and Selaginella. McLean regards it as representing a 

 stage in the reduction of the primitive free-living Lycopod gametophyte, 

 towards the condition obtaining in the seed of Lepidocai'pon. The 

 tballus was not produced until after the megaspore had been shed. It 

 developed outside tlie spore, but remained attached to the spore-wall at 

 its base : and in form it resembled the prothalli of modern hetero- 

 sporous ferns. The gametophyte of Bothrodendron was more primitive 

 than that of Lepidodendron, where the archegonia developed inside the 

 spore. 



Zygopteris Grayi.J — D. H. Scott gives an account of the fossil fern 

 Zygopteris Grayi Williamson and of its relationships. The fossil remains 

 occur rarely in Lancashire coal-beds. A new specimen found at Shore, 

 Littleborough, has been cut into sections, and shows a five-ray stellate 

 stele, the corresponding 2/5 phyllotaxis, leaf-trace bundles with axillary 

 slioots, scale-leaves or aphlebiai, and adventitious roots. The character- 



* Rep. Brit. Assoc, 1910 (1911) p. 784. 



t New Pbytologist, xi. (1912) pp. 305-18 (2 pis. and figs.). 



: Hep. Brit. Assoc. Portsmouth, 1911 (1912) pp. 568-9. 



