1897] NOTES AND COMMENTS 157 



once dominant group. There are only nine genera with about 

 seventy-five species, but the order is widely distributed in the 

 warmer parts of the earth, though individual genera and species 

 have a very limited distribution. The old world has five genera, 

 the new world four, but America possesses by far the greater 

 number of species, Central America and Mexico being the richest 

 areas, while Australia is the largest centre in the old world. 

 Cijcas (sixteen species) is the most widely-spread type, occurring 

 in the warmer parts of Asia up to south Japan, in Australia, 

 Polynesia and the Malagasy Islands. Stangcria and Bowenia are 

 monotypic genera from Natal and Queensland respectively. Dioon 

 has two species in Mexico ; Encepltalartos, twelve in South and 

 tropical Africa ; Macrozamia, fourteen in Australia. Zamia is the 

 largest genus with thirty species, and is found from Peril to the 

 West Indies and Florida ; Ceratozamia is Mexican with six species, 

 and Microcycas is a monotypic genus from Cuba. But a much 

 larger number of fossil genera have been described, chiefly from 

 leaves, though fruits and other reproductive organs are also known. 

 Tims Engler in his Pflanzenfamilicn enumerates twenty-three 

 " more important " ones found almost exclusively in Europe, but 

 occasionally in Greenland and Spitzbergen. Our nine genera are 

 obviously scattered remnants of a once large and dominant family. 

 Even individuals are isolated ; except in the case of species of 

 Cycas they are few and far between. 



In the June number of the Botanical Gazette, H. J. Webber gives 

 an account of his investigations into the structure and behaviour of 

 the pollen-tube in a species of Zamia. One of his figures shows 

 a peculiarity in the growth of the tube, which at first penetrates 

 the nucellus for a short distance and then resumes growth at the 

 other end, that, namely to which the grain is still attached. The 

 important generative cell remains at the pollen-grain end in which 

 it is carried down into the cavity above the archegonia or female 

 organs. Webber describes two centrosome-like structures in this 

 generative cell, the function of which is doubtful. The most 

 interesting part of his communication is contained in a note 

 which records the discovery, as the paper was going through the 

 press, of motile antherozoids. As to how or where they arise, 

 whether they are or are not in any way connected with the 

 strange bodies in the generative cell, we are left completely in 

 the dark, and can only hope for a continuation in our next. 



The Fossils of the English Chalk Pock 



Thanks to Mr Henry Woods, we have now an intelligent and 

 careful account of the mollusca of one zone of the Cretaceous 



