410 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Structure and Development. 
Vegetative. 
Normal and Abnormal Germination of Grass-fruits. — J. Zinn 
( Ann . Rep. Maine Agric. Exp. Slat., 1920, Bull. 294, 197-216,44 figs.). 
“ An account of the processes that take place at the time of emergence 
of the radicle of hulled grass-fruits from the surrounding tissues.” The 
penetration of the pericarp is a purely mechanical process due to the 
pressure of the embryo, whereby the tissues break away at a certain point 
and usually in a certain direction. Normally the coleorhiza breaks 
through the base of the fertile glume at a region where the resistance is 
diminished by modification of the epidermal and hypodermal cells : the 
latter are pushed apart, the sclerenchymatous elements being entirely 
uninjured, and the epidermis more or less so, but the fibro-vaseular 
bundles are invariably broken. In abnormal germination external 
mechanical factors due to artificial conditions hinder the growth of the 
radicle in the normal direction, and growth takes place in the direction 
of least resistance. Abnormal germinations are absent or rare when 
grasses are grown in natural soil, and under normal conditions there is 
no dying off of the radicle within the glume. The rupture of the 
glumes by the coleorhiza is due to the turgescence of the latter aided 
by the short thick walls of its apical tissues. The coleorhiza also acts 
as a protective organ for the young radicle, and by means of its hairs 
or trichomes assists in fastening the seedling to the soil. The formation 
of hairs is a general feature of the coleorhiza of grasses. The radicle 
itself passes from the coleorhiza through a longitudinal lateral opening, 
without injuring the cells in any way. S. G. 
Vascular Anatomy of Seedlings of Phaseolus. — J. A. Harris, 
E. W. Sinnott, J. Y. Pennypacker, and G. B. Durham (. Amer . 
Journ. Bot. y 1921, 2, 63-102, 12 figs.). A comparative and biometric 
study of the vascular system of dimerous and trimerous seedlings of 
Phaseolus vulgaris. In dimerous seedlings the root is tetrarch with 
four protoxylem poles, from which arise eight bundles which pass 
through the hypocotyl to the cotyledonary node, where two strands are 
given off to each cotyledon, while the remaining six divide to form the 
typical twelve bundles found in the epicotyl. The trimerous seedlings 
differ in having six protoxylem poles, twelve bundles in the hypocotyl, 
nine primary bundles, and fourteen to eighteen permanent bundles in 
the epicotyl. Both types of seedlings may have additional intercalary 
bundles in the hypocotyl. The trimerous seedlings show a greater 
variability in the number of root-poles, but the deviation in the inter- 
calary bundles is more marked in dimerous seedlings. In the central 
part of the hypocotyl the dimerous seedlings vary more greatly in the 
number of bundles, while in the epicotyl the reverse is the case. From 
the above results the authors conclude : — (1) That external differentia- 
tion is accompanied by profound differences in internal anatomy ; 
(2) that anatomical characters vary greatly in series of individuals 
which are genetically highly homogeneous ; (3) “ that variation in 
anatomical structure is not constant for the plant as a whole, but may 
