iqi2] THOMPSON— STOMATA OF CRETACEOUS CONIFERS 67 



so-called guard cells are really the commonly occurring accessory 

 cells. The only recorded exception to the remarkably uniform 

 organization of the stoma in the Embryophyta thus disappears. 



The writer is indebted to Professor Jeffrey for the material 

 used in this investigation, which was carried on under appoint- 

 ment as an 1851 Exhibition Science Research Scholar of the Uni- 

 versity of Toronto. 



Harvard University 

 Cambridge, Mass. 



EXPLANATION OF PLATES V AND VI 



Fig. 1. — Frenelopsis Occident alls: stoma in surface view, showing the 

 rosette of projections; X333. 



Fig. 2. — The same: vertical section through a stoma, showing the pro- 

 jections into stomatal cavity; X250. 



Fig. 3. 



guard 



accessory cells; X250. 



Fig. 4. — The same: another stoma with distinct guard cells; X 250. 



Fig. 5. — The same: camera lucida drawing of stoma from beneath, show- 



:wo guard cells above the accessory cells. 



Fig. 6. — Agathis bornensis: vertical section of base of leaf, showing two 



guard cells sunken 



X333- 



Fig. 7.— The same: section parallel to the surface, showing stomatal 

 opening surrounded by four accessory cells; X333- 



Fig. 8.— The same: section parallel to the last but deeper— below the 

 accessory cells and including the two guard cells; X333- 



Fig. 9. — Androvettia statenensis: surface view of epidermis; X63. 



Fig. 



10. 



guard 



accessory cells; X250. 



Fig. 



11. 



guard cells have disappeared 



X250. 



Fig. 12.— Br achy phyllum macrocarpitm: section parallel to the surface, 

 I accessory and guard cells; X125. 



