ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 599 



Summer and Winter Leaves.* — J. P. Stober has studied the re- 

 spective peculiarities of summer and winter leaves in a large number of 

 herbaceous plants. The author made transverse sections throutrh the 

 centre of leaves taken from different plants of the same species at 

 different times and in different habitats. The differences were most 

 clearly marked in plants from different habitats, and were observed in 

 the epidermal hairs, walls and cells ; also in the cuticle, stomata, blade, 

 and collenchyma. In both summer and winter forms hairs are more 

 abundant in the upper than in the lower leaves, but usually are more 

 abundant in summer than in winter leaves. Stomata are more abundant, 

 rounder, and more numerous in summer than in winter. The winter 

 leaves have larger epidermal cells with sinuous lateral walls. The blade 

 of winter leaves is usually thicker than that of summer leaves, unless the 

 latter are of xerophytic type. Winter leaves have thicker epidermal 

 walls and cuticle than summer ones except in xerophytes. The palisade 

 parenchyma is better organized in summer leaves, but the thickness of 

 the palisade cells is greater in winter leaves. There is a greater amount 

 of collenchyma and more air-spaces in winter than in summer ; scleren- 

 chyma is equally developed in summer and winter, but conductive tissue 

 better in winter. On the whole winter leaves are more mesophytic in 

 structure than summer leaves. 



Reproductive. 



Gametophytes of Taxus canadensis.! — A. W.Dnpler is investigating 

 the morphology of this American representative of the Old World Taxus 

 baccata. He finds that in general the gametophyte history agrees with 

 that reported for T. baccata. Microspore formation takes place in the 

 autumn ; there are no indications of prothallial cells. The pollen-grain 

 is uninucleate when shed. The pollen-tube penetrates the nucellus very 

 rapidly and enlarges excessively about the female gametophyte. Three 

 divisions take place in the development of the male gametophyte ; the 

 body-cell divides into two unequal male cells, the larger of which 

 functions in fertihzation. Several megaspore mother-cells are formed, 

 of which only one usually functions, although two of them may form 

 megaspores. The megaspore mother-cell is the usual winter condition, 

 but megaspores may be formed, and the female gametophyte may consist 

 of several free nuclei before winter. Following the free nuclear stage 

 of the female gametofiliyte, radial walls come in, closing the cavity before 

 the appearance of periclinal walls. The archegonia appear early in the 

 endosperm ; the central cell is the functional Qgg, no ventral canal cell 

 or ventral nucleus being formed. More than one female gametophyte 

 in an ovule is common ; as many as live were observed. In fertilization 

 the nuclear contents of the pollen-tube are discharged into the ag^ ; a 

 cytoplasmic sheath is formed about the two fusing nuclei. From pollin- 

 ation to fertilization may be as short as one month. Mature seeds 

 have been collected six weeks later. 



* Bot. Gaz., Ixiii. (1917) pp. 89-109. 



t Bot. Gaz., Ixiv. (1917) pp. 115-36 (4 pis.). 



