1915] CURRENT LITERATURE 325 
green is a simple Mendelian recessive to the normal, and a similar result was 
obtained in crosses between the striped forms known as Zea japonica, in 
crosses with the normal green strains, the striped being recessive to normal, 
though in the latter cross there is some confusion when certain differences in 
aleurone colors are also involved in the same cross. The exact nature of this 
relation between aleurone colors and leaf colors was not worked out. Crosses 
between striped plants and chlorina, and between striped and yellowish white 
yielded in each case normal green plants, owing to the bringing together of 
complementary factors. 
Mites also made a study of the chloroplasts in the several strains with 
which he worked. He could find no plastids in the pure white seedlings, and 
only a few small plastids in the yellowish white, which became more numerous 
and larger as the plants grew older, until they resembled, in the better developed 
individuals, the normal condition. In the case of striped-leafed plants, the 
arrangement of the plastids showed a sharp distinction between the cells of 
the green portions of the plants and those of the white stripes—G. H. SHULL. 
he physiology : pollen.—In his work on the physiology of pollen, 
Toxucawas dealt with three main points of interest: factors determining 
germination, factors jane the direction of the pollen tube, and factors 
determining the rate and extent of the growth of the pollen tube. The investi- 
gator adds evidence against the views of Mottscu and of Burcu that specific 
substances on the stigma generally determine whether the pollen will germinate 
or not. Already many cases have been found in which the physical conditions 
are the important ones in determining germination. Jost showed for various 
species in several families that restricted water supply is the main requirement 
for the germination of the pollen. He secured this condition by germination 
of the pollen in a saturated atmosphere or on leaf epidermis or parchment 
paper. ToxucGawa adds many more to the list. He has evidently failed, how- 
ever, to notice the work of MarTIN,§ which shows the important newly discov- 
ered fact that conditions giving a free water supply to the stigma may lead to 
sterility. This holds for alfalfa and certain clovers in the central Mississippi 
alley when pollination occurs at moist or wet periods. 
he author confirms the statement that sugars and proteins are important 
chemotropic substances for the pollen tube. In certain plants (Narcissus 
Tazetti and Prunus mume) sugars are effective, and in other (Camellia japonica) 
proteins. He concludes that chemotropism determines the entrance of the 
tube into the stigma canals and the micropyle, and that the tube is directed in a 
physical manner in the rest of its course. 
The conditions affecting growth of the pollen tube are considered in 
relation to their significance in determining self-sterility and failure to 
’ Toxucawa, Y., Zur Physiologie des Pollens. Jour. Coll. Sci. Tokyo 35:1-35. 
figs. 2. 
® Bor. Gas. 56:112-126. 1913. 
