1897] NOTES AND COMMENTS £57 
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. 
Cycas (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. Stangeria and Bowenia are 
monotypic genera from Natal and Queensland respectively. Dioon 
has two species in Mexico; Hncephalartos, twelve in South and 
tropical Africa ; Macrozamia, fourteen in Australia. Zamia is the 
largest genus with thirty species, and is found from Peru 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. 
Thus Engler in his Pflanzenfamilien 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 Rock 
THANKS to Mr Henry Woods, we have now an intelligent and 
careful account of the mollusca of one zone of the Cretaceous 
