155 



VI. On the Cuticles of some Recent mid Fossil Cycadean Fronds. By H. Hamshaw 



Thomas, M.A., F. G.S., Curator of the Botanical Museum, Cambridge, and Nellie 

 Bancroet, B.Sc F.B.S., 1851 Research Scholar, Newnham College, Cambridge. 



(Plates 17-20. and 32 Text-figures.) 



Read 6tli November, 1913. 



CONIENXS. 



Pago 



I. Introduction 1^^ 



II, Cuticles of some Recent Cycads ■ • ■ • 



(a.) Material and Methods 

 (6.) Previous references • 



(c.) Description of the Cuticles 



157 

 157 



157 

 158 



i. Introduction 1^^ 



ii. Detailed description 15" 



iii. General summary of the structure of the recent Cuticles 174 



^ li I 



III. Cuticles of Fossil Cycadean Fronds 



(a.) Previous observations on cuticular structure 177 



(6.) Detailed description 



179 



(c.) The Cuticles of some other types of Fossil Cycadean fronds 194- 



(d.) Summary of the structure of the Fossil Cuticles 195 



IV. Comparison of the Cuticular Structure of Hecent and Fossil C}cadeau 



Fronds, with notes on that of other Gymnosperms 197 



I. INTRODUCTION. 



In an investigation of the cuticles of recent and fossil Cycads onr attention is 

 principally concentrated on the form and structure of the stomata, a study of which has 

 attracted many ohservers. The physiological functions of the guard-cells are so important, 

 and their shape and action are so uniform in plants of widely separated classes, that they 

 may be regarded as highly adapted to their special work, and as structures which were 

 evolved at a comparatively early period in phylogenetic development. But while the 

 morphology of the stomata is uniform, many differences of structure, especially of 

 thickening, do exist, rendering the work of classifying stomata by no means easy. One 



g, \xyj v.aj.ou, X v/ixvAwi *"J3 



tructur 



of the few general attempts to make a survey of the whole range of these 

 to classify them in groups, and to find broad general tendencieB in their variation, 

 that of Porsch (1905), who has introduced a conception of a phylogenetic ground-plj 

 modified by adaptations to external conditions. The idea that stomatal structui 



SECOND SERIES. — BOTANY, VOL. VIII. 



2b 



