A. A. MERLIN ON TRICERATIUM. 267 



temperature, the influence of light and other refinements which 

 must be observed in some cases if success in cultivation is to be 

 attained ; but the more advanced student will find full information 

 in the larger treatises on Physiological Botany, monographs and 

 special papers. 



Note on Certain Minute Structure observed in some 



Forms of Triceratium. 



By a. a. Merlin, F.E.M.S. 

 {Read March 2\.st, 1902.) 



A variety of IViceratiuin ^;rt?*rt7/e^z<.7?i from the Oamaru 

 deposit, resembling the ordinary form in size, shape and general 

 appearance, but not identical in detail, has been found to possess 

 a delicate lace work structure apparently covering the whole of 

 the silex composing the upper surface of the valve, and extending 

 to and closely surrounding the primaries. Subsequently a similar 

 but even finer network v>7as observed on the outer surface of a 

 typical Ti'iceratium 2Xirallelum. This is an excessively faint and 

 difficult object, and is close to the limit of visibility with a fine 

 Zeiss 3-mm. apochromat of N A. 1*426, illuminated by the full 

 cone of Powell's dry adjustable apochromatic condenser. Later, 

 signs of the existence of an identical network were noticed on a 

 Triceratium glandiferu'ni Grun, which could only be resolved and 

 held for brief intervals, after long rests to the eye in the dark, by 

 the employment of the 1*426 objective and a solid axial cone of 

 about ]Sr.A. 1*3 from Watson's oil-immersion condenser. I believe 

 this to be the most faint and evasive of all the diatomic structures 

 I have observed, but possibly certain other valves of this species 

 may prove easier than the specimen referred to. 



From the indications, there can be but little doubt that the 

 appearances seen in the above-mentioned forms represent really 

 existent structure on the upper surface of the silex, and are due 

 to no ghostly diffraction effects. 



All the specimens alluded to were mounted in styrax. 



Joarn. Quekett Microscopical Club, Ser. 2, VoL VIII. , No. 50, Ajn-il 1902. 



