152 THE JOURNAL OF INDIAN BOTANY.
Finally, the substance of the mother-cells is divided into tetrads of spores
by invaginations, as in animals, regardless of whether the spindle fibres per-
sist or have already disappeared. No cell plate formation in the usual manner has been observed. As the pollen grains are maturing, the tapetal cells disorganize into a tapetal Plasmodium, a condition regarded as uncommon for angiosperms.
The paper leaves one with the feeling that the author has distinctly furthered our knowledge of the process of reduction, and of the mechanics of heredity. The closing sentence is one the spirit of which might well be taken to heart by all engaged in scientific investigation ; " it is considered that the study of variations in the behavior of the chromosomes has been too much neglected, and that any account is incomplete which does not include a record of the conditions rarely or infrequently observed, as well as of those which
seem to fall into the usual order of events."
W. D.
Distribution.
Hitchcock, A. S., Floral aspects of the Hawaiian Islands. Annual report of the Smithsonian Institution, 1917. p. 4J-9* (Just received).
This is a semi-popular account of the flora of these islands and contains much interesting matter. The writer is much struck with the number and variety of ornamental plants which he met at Honolulu, practically all of foreign origin. He states indeed that at least on the plains, the native flora has been almost exterminated by introduced plants, many of them weeds. This is in accordance with Charles Darwins expectation of the superiority of continental and widely distributed species over those of a small area. Among these introduced plants are several species familiar to us in Indian gardens, e,g., Cassis fistula, C. nodosa, varieties of Hibiscus, Acalypha, Aralia and the common Croton (Uodiaeum variegatum) and of course the S. American Bougainvillea. The islands have not escaped those pestiferous weeJs, Opuntia, and Lantana, but Acacia farnesiana and Lucaena glauca, though introduced some years ago and throughly naturalised have not become troublesome. Coming now to the natural or indigenous flora, the most striking are the giant Lobelias, of which there are as many as 100 species, some attaining a height of 40 feet. Ferns of all sizes abound, the tree-ferns running up to even 30 feet, though usually shorter. What is apparently a strongly zerophytic plant is the " silver sword", Argyroxiphium sandwicense, which has numerous sharp pointed leaves covered with silvery-white closely appressed wool. The plants grow in dense tussocks from a few inches to two feet in diameter, on cinder cones and other arid spots, and in the distance look like sheep. Similar tussocky plant are common in other desert regions. An interesting feature of the flora is the poverty in species of certain world-wide families. Thus there are practically no orchids, only three small terestrial and rare species being known ; the palms are represented by ten species only of the single genus Pritcardia ; the Melastomaceae are entirely absent though so abundant in tropical America ; and the Compositae and Labiatae, large universally distributed families, and the former usually abundant in mountainous country, have only a few species. Considering the tropical position of the islands, and the large climatic differences caused by the presence of mountains
