Band 131. Nr. 9. XXXVII. Jahrganp:. I. Bd. Nr. 9. 



Botanisches Centralblatt 



Referierendes Organ 



der 



Association Internationale des Botanistes 

 für das Gesamtgebiet der Botanik. 



Herausgegeben unter der Leitung 

 des Präsidenten: des Vice- Präsidenten: des Secretärs: 



Dr. D. H. Scott. Prof. Dr. Wm. Trelease. Dr. J. P. Lotsy. 



und der Redactions-Coinmissions- Mitglieder : 



Prof. Dr. Wm. Trelease, Dr. C. Bonaventura, A. D. Cotton, 



Prof. Dr. C. Wehraer und Dr. C. H. Ostenfeid. 



von zahlreichen Specialredacteuren in den verschiedenen Ländern. 



Dr. J. P. Lotsy, Chefredacteur. 



No. 9. 



Abonnement für das halbe Jahr 15 Mark 



durch alle Buchhandlungen und Postanstalten. 



1916. 



Alle für die Redaction bestimmten Sendungen sind -zu richten an: 

 Rjdaction des Botanischen Centralblattes, Haarlem (Holland), Spaarne 17. 



Holden, R., On the relation between Cycadites and Pseudo- 

 cycas. (New Phytologist. XIII. 10. p. 334—340. Dec. 1914.) 



Nathorst in 1907 established the genus Pseudocycas for cer- 

 tain cycadean fronds formerly referred to the genus Cycadites. Thej' 

 differ from the latter genus in the possession of a double instead of 

 a Single midrib, and in the fact that the pinnules are not narrowed, 

 but if anything broadened at the point of attachment to the rachis. 

 Further the stomata are confined to the ridges formed by the double 

 midrib and to the furrow between; the epidermal cells are in long 

 rows, and their walls are sinuous. 



In the present paper two species of Cycadites (C. rectangtilaris 

 a Rhaetic sp?cies, and C. Saportae an English Wealden species) have 

 been examined with special reference to the epidermal characters. 

 It is shown that they should be transferred to the genus Pseudo- 

 cycas since they differ from the members of that genus only in the 

 presence of additional stomata. It has been shown by Thomas and 

 Bancroft that there is a general cycadean type of Stoma which 

 varies but slightly in all living and fossil forms. Among the various 

 features may be mentioned number of accessorj'- cells, shape and 

 size of guard cells, etc. Between extant and extinct, however, there 

 is a further point of difference, dependent on the fact that in the 

 former the xerophytic habit has caused an almost universal sinking 

 of the guard cells with the consequent interposition of one or more 

 series of intercalary cells between them and the accessory cells 

 proper, while in the latter, at least in the Bennettitales group, the 

 stomata open directly on the surface. On this criterion the genus 

 Cycadites should be included in the Bennettitales group. 



Botan. Centralblatt. Band 131. 1916. 14 



