ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 189 



7. In extreme cases of abortion in the microsporangia only one spore 

 survives, and grows to about 16 times the size of the normal microspore. 

 The aborted tetrads remain as in the megasporangium, but are larger 

 and better developed, indicating a more prolonged contest for supremacy. 



8. In plants kept from sporocarp-formation until September 10, many 

 microsporangia developed secondary megaspores, so called because they 

 are formed after the first or primary ones. Such megaspores are inter- 

 mediate in size and are also more nearly the spherical shape of the 

 microspores. 9. In a few cases the megaspores did not develop a peri- 

 nium. but enlarged considerably and became full of starch. 10. In 

 normal plants, and in all cultures, a homosporous tendency is found, 

 shown by the formation of microspores in the megasporangia, especially 

 in those' most distant from the nutritive supply. 11. Marsilia may be 

 made to repeat, uuder culture, all the phases in the development of 

 heterospory reported by Williamson and Scott for Calamostachys Bin- 

 neyana and 0. Casheana, and in addition to produce a megaspore of 

 intermediate size. 



Fertilisation of Fern-prothallia.* — G. Perrin gives a brief account 

 of some experiments made upon fern-prothallia in order to test the ap- 

 plicability of Traube's theory that the rapidity of osmosis and the state 

 of equilibrium dependent upon it is above all a function of the differ- 

 ence of the superficial tensions of the liquids present. Antherozoids of 

 ferns in pure water with a superficial tension of 7 • 5 mg. move about 

 without change of form or volume ; but in solutions of lower superficial 

 tension they move more slowly, swell, lose their form, and not rarely 

 burst. Thus under the latter conditions fertilisation is fatally hindered. 

 In the experiments described, solutions, with the surface-tension reduced 

 by the addition of various infinitesimal amounts of bile-salts to pure 

 water, were employed, and produced a corresponding reduction in the 

 percentage of archegonia fertilised. Through swelling or bursting the 

 antherozoids tend to fail to penetrate into the archegonia. 



Cytology of Varietal and Hybrid Ferns.f — J. B. Farmer and L. 

 Digby discuss the cytological features exhibited by certain varietal and 

 hybrid ferns, and in particular Polypodium Schneideri, which is stated 

 to be a hybrid between P. aureum and P. vidgare var. elegantissimum. 

 In their summary they say that : — 1. The view that Polypodium 

 Schneideri is of hybrid origin receives support from a study of its 

 cytology. 2. The nuclei of P. aureum are one-third smaller than those 

 of P. vidgare. The number of chromosomes in P. aureum is about 

 34 to 36, in P. vidgare about 90. In P. Schneideri they vary between 95 

 and 125. 3. In P. vidgare var. elegantissimum many abortive spores 

 are produced, in P. Schneideri all are abortive. This sterility is asso- 

 ciated with degeneration of the cytoplasm and of the nuclear apparatus. 

 4. The achromatic spindle in P. aureum, etc., is bipolar, in P. vidgare 

 mostly quadripolar, in P. Schneideri either bipolar or quadripolar, usually 

 the latter. 5. The spindle is formed from a differentiation of the cyto- 

 plasm (kinoplasm) and is influenced in its distribution by the aggregation 



* Comptes Rendus, cxlix. (1909) pp. 1086-7. 

 t Ann. Bot., xxiv. (1910) pp. 191-212 (3 pis.). 



