RECENT ADVANCES IN SCIENCE 639 



petroleum depends chiefly on the conditions of temperature 

 and pressure under which it was formed, and on chemical 

 changes due to the contemporaneous or subsequent contact 

 with sulphur. 



In a comprehensive work on the interrelations of fossil fuels 

 (Proc. Amer. Phil. Soc. 1916, 45, 21-203) J. J. Stevenson brings 

 together the known facts regarding recent and Pleistocene peats, 

 and Tertiary coals. He emphasises the wide area on which peat 

 is at present being formed, an area greater than that covered by 

 carbonaceous deposits in any other period of similar duration. 



BOTANY. By E. J. Salisbury, D.Sc, F.L.S. 



Morphology. — The interpretation of the grass embryo has long 

 been a matter of dispute amongst morphologists. Worsdell 

 has recently described some abnormal seedlings of maize in 

 which the coleoptile exhibited more or less marked bifurcation 

 of the apex (Annals of Botany, vol. xxx. pp. 509-25, 191 6). 

 In discussing the interpretation to be placed on this phenomenon 

 the author deals with the general question of the morphology 

 of the grass embryo. The conclusion is arrived at that the 

 scutellum is to be regarded as the lamina of the cotyledon and 

 the coleoptile, or plumular sheath, as its ligule. With Cela- 

 kovsky the author regards the epiblast as comparable to the 

 auricles present in the foliage leaves of some grasses . In such 

 cases as have been recorded of monocotyledonous embryos with 

 two cotyledons (Agapanthus, Cyrtanthus) the second cotyledon 

 is explained not as a reversion but as due to excessive develop- 

 ment of the sheath of the normally present terminal cotyledon. 

 The forked coleoptile of the seedlings described is taken as 

 indicative of the derivation of the ligule from a pair of stipular 

 appendages. 



Takeda (Annals of Botany, vol. xxx. pp. 197-214, 191 6) 

 has recently investigated a number of the four-leaved bed- 

 straws and their allies in relation to the morphology of the 

 nodal structure. He finds that in the development of the 

 seedlings of species with normally six leaves at the node the 

 four-" leaved " condition precedes the six-leaved. On the 

 assumption that the ontogeny recapitulates the phylogeny of 

 the group, the conclusion is arrived at that the four-leaved 

 condition (two true leaves and two stipules) is the primitive 

 one for the Stellatae. In the four-" leaved " species described 



