572 SUiMMARY OF CURRENT RESEARCHES RELATING TO 



there are characteristic bands of colourless parenchyma-cells, probably 

 utilized in assimilation ; the stomata are not depressed. Themeda 

 avenacea has stiff, rigid leaves, owing to the extremely well-developed 

 hypodermal fibres ; the buUiform cells are well marked. The chief 

 serophytic features of Panicum flavidum are dorsal stomata, bulliform 

 cells, well-developed hypoderma, large and numerous xylem elements. 

 P. decompositum is less xerophytic than the previous species, and is the 

 only Panic-grass examined having bands of colourless parenchyma for 

 aiding assimilation. P. Uucophseum is still less xerophytic ; the 

 hypoderma is poorly developed, the bundles are small, and the bulliform 

 cells less well marked. The least xerophytic of these Panic-grasses is 

 P. Benihami. In Neu,raclme MitchplUana the chief xerophytic features 

 are a well-developed hypoderma, the large number of primary bundles, 

 bulliform cells, the position of the stomata, the presence of tricliomes. 

 C/don's acicidaris presents typical xerophytic features in the development 

 of the hypoderma, in the bands of colourless parenchyma cells, the 

 position of the stomata, and in the bulliform cells. Eragrostis lacunaria 

 has trichomes, bulliform cells, and a well-developed hypoderma ; 

 E. curvida, a cultivated species, has similar characters, but the 

 hypoderma and xylem elements are better developed, probably owing 

 to the necessity for giving rigidity to the very long leaf. 



Bordered Pits and Ascent of Sap.* — I. W. Bailey has studied the 

 bordered pits of Conifers in order to ascertain if the membranes form 

 complete septa entirely impervious to finely divided solids and undissolved 

 gases. Numerous sections of the wood of Larix and Sequoia were 

 examined, and it was found that the membranes were clearly perforated, 

 but the detailed structure was obscured l»y the overhanging walls. 

 Aqueous solutions containing finely divided carbon could be made to 

 pass freely through the membranes. The presence of perforations was 

 also indicated by the fact that large quantities of gas could be forced 

 through the pits of tracheides already saturated with sap. The surface 

 tension of sap in the pit-menibraues is proved to be less than three 

 atmospheres. The tension hypothesis, according to which a pressure of 

 five to twenty atmospheres is required in order to maintain continuous 

 columns of water in trees, is thus shown to be untenable. 



Reproductive. 



Embryogeny of Cooperia.t — M. B. Church has studied the develop- 

 ment of the embryo-sac and embryo of Gooperia Drummo7idii. The 

 writer finds that the primitive archesporial cell is of hypodermal origin, 

 and develops at the expense of the nucellus into a large oblong cell. 

 No tapetal cells could be found. Megaspore-formation was of the type 

 usual for the Liliacea?, and it seems probaljle that reduction-division 

 occurs with the division of the one-celled stage. Bv division of the 



» Bot. Gaz., Ixii. (1916) pp. 133-42 (1 pi. and 2 figs.). 



t Bull. Torrey Bot. Club, xliii. (1916) pp. 397-405 (2 pis.). 



