6oo 



NATURE 



January 28, 19 15 



toothless ichthyosaurs is the nature of their food, 

 which was almost certainly different from that of their 

 stronglv toothed Liassic precursors, which appear to 

 have been less well adapted for a pelagic life. It is 

 not that the heavily armoured ganoid fishes of earlier 

 formations had died out,ir^"-wTTness the presence of 

 Lepidotus in the Oxf^dian ; and it may be that the 

 ichthyosaurs of thatx^epoch fed on belemnites instead 

 of fish. If |iui!__be so, the Cretaceous toothless ptero- 

 dactyles may likewise have made an analogous change 

 in their diet, as compared with that of their well- 



damage at particular seasons. The observations re- 

 corded in this paper are of general interest, as the 

 plant chosen for investigation was wheat, and the 

 following are the chief results obtained. 



Grass culms show in general two periods of 

 growth — a preparatory period characterised by short 

 internodes carrying scales or under-sized leaves, and 

 a subsequent period of vigorous growth characterised 

 by long internodes carrying well-developed leaves. 

 In the average primary culm (i) the same number of 

 leaf-bearing internodes is produced in these two 



Skeleton of Ophthalmosaurus icenicus from the Oxford Clay exhibited in the Geological Departr-.tnt of the British Museum (Nat. Hist.). Reproduced 



from the Museums Journal. 



toothed ancestors, only in their case it may have been 

 merelv from hard-scaled to soft-scaled fishes. 



R. L. 



DEVELOPMENT OF THE CULMS 

 GRASSES. 



OF 



AN important paper by Mr. R. S. Hole, forming 

 Forest Bulletin No. 25 of the Indian Forest 

 Research Institute, deals with the development of the 

 culms of grasses. The author points out that the 

 generalisation, based upon the study of grasses and 

 cereals of temperate climates, that the culms are 

 annual does not hold good in the case of various 

 economically important species which are dominant 

 in the savannah lands of Indian forests ; hence the 

 discovery of a method by means of which the age 

 of the culms of any particular species can be readily 

 determined is a matter of practical importance bear- 

 ing directly on such questions as the selection of the 

 best rotation to adopt in the case of grasses worked for 

 paper pulp or the liability of certain species to fire 



NO. 2361, VOL. 94] 



stages, but the period of preparatory growth is ap- 

 proximately three-fourths of that of vigorous growth ; 

 (2) the average number of long internodes produced is 

 approximately equal to the number of months in the 

 period of vigorous growth, and this number is practically 

 the same whether calculated from the primary culms 

 alone, from the axillary culms alone, or from a mix- 

 ture of these as found in the final crop. In the older 

 axillary culms (i) both growth periods, but more 

 especially the preparatory period, are shorter than 

 those of the primary culms, and there is little differ- 

 ence between the two classes of culms as regards the 

 date of ripening gi-ain ; (2) the number of leaf-bearing 

 short internodes is approximately half the number of 

 the long internodes, and the preparatory period of 

 growth is approximately half the vigorous growth 

 period. The author thus obtains for both annual and 

 perennial grasses the generalisation that the average 

 number of leaf-bearing long internodes produced in a 

 culm — that is, excluding the apical segment terminat- 

 ing in the inflorescence — is approximately equal to 

 the number of months comprising the period of 

 vigorous growth. F. C. 



