ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 221 



variation in the shape of the leaves on the plant, variation in the 

 colour of the anthers, and the occurrence of plants possessing characters 

 found in two distinct species growing near by, may all be taken as 

 evidence of hybridity, or progressive species. 



The fact that Crataegus plants seem to come true to type when grown 

 from seed is a stumbling block in the way of a hybridity theory. How- 

 ever, it is possible that Crataegus hybrids are stable, and come true to 

 type when grown from seed. It cannot be said that they have been 

 tested thoroughly until many mature plants have been grown. 



Some of the points just made may be taken as evidence of muta- 

 tions, but the best known mutants are not as irregular in characters as 

 many of the species of Crataegus. 



CRYPTOGAMS. 



Pteridophyta. 

 (By A. Gepp, M.A., F.L.S.) 



Pteridophytal Origin of so-called Algal Coals.* — E. C. Jeffrey 

 has investigated the nature of some supposed algal coals. By means 

 of the slow action of concentrated acids, alkalis, etc., applied for weeks 

 at a time, he has succeeded in softening the coal sufficiently to admit 

 of microtome-sections, and even of serial sections, being cut. He gives 

 the following summary of his conclusions. 1. The organisms found in 

 abundance in boghead coals are not of the nature of colonial gelatinous 

 algaj, as has been asserted by Renault, Bertrand and Potonie, on the 

 basis of the examination of a small number of insufficiently thin sections 

 of such coals. 2. The bodies in question, as revealed in thin serial 

 sections, made by improved technique on the microtome, are spores of 

 vascular cryptogams. 3. The proof that the constituent micro-organisms 

 of boghead coals are not algae but spores, overthrows the algal hypothesis 

 of the origin of petroleum and similar substances. 4. It appears clear 

 that petroleum products have been derived, mainly at any rate, from 

 the waxy and resinous spores of vascular cryptogams laid down on the 

 bottoms of the shallow lakes of the Coal Period. These lacustrine 

 layers, either as cannels, bogheads or bituminous shales, according to the 

 sporal composition and the admixture of earthy matter, are the mother- 

 substance of petroleum. Pressure and temperature either separately or 

 combined, in the presence of permeable strata, have brought about the 

 distillation of petroleum from such deposits. 



Nomenclature of Nephrodium.f — W. N. Clute calls attention to 

 another revolutionary change which threatens the nomenclature of the 

 large group of ferns ranged till a few years ago under the well-known 

 generic names Nephrodium or Lastreea, but latterly transferred to the 

 revived and prior name Dryopteris. It now appears that all the species 

 will have to be renamed once more, since J. A. Niewland has shown in 

 the June number of the American Midland Naturalist that before 



* Proc. Amer. Acad. Arts and Sciences, xlvi. (1910) pp. 273-90 (5 pis.). 

 t Fern Bull., xviii. (1910) pp. 82-92. 



April 19th, 1911 Q 



