ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 711 



March 25-27. The single megaspore begins to germinate in the middle 

 of February ; 8—16 and sometimes more free nuclei are formed. 

 Several pollen-tubes begin to develop from a grain, but only the one 

 which comes in contact with the stigma continues development. The 

 tube generally enters through the micropyle, but sometimes pierces the 

 nucellus at various places, and even passes down the funicle ; it may 

 also branch profusely, but apparently only in the case of belated tubes. 

 The male cells leave the grain as soon as the tube is 1 mm. long, re- 

 maining close to its tip, and were always found side by side ; the tube 

 nucleus does not leave the pollen -grain. Double fertilisation was 

 noted, occurring from March 28-31, the first male cell fusing with the 

 endosperm nucleus. The latter generally divides before the fertilised 

 egg, forming large, multi-nucleolate nuclei. The embryo is of the 

 massive type, the suspensor cell enlarging but little. An antipodal egg 

 is not uncommon. Two embryos are occasionally found in the same sac, 

 and two embryo-sacs are sometimes found in a single nucellus, each 

 with an egg-apparatus. Chalazogamy was not certainly found, but 

 there are indications of its occurrence. 



Physiology. 

 Nutrition and Growth. 



Supply of Water to Leaves on a Dead Branch.* — H. H. Dixon 

 concludes that it is unnecessary to attribute to the cells of the stem a 

 special function in the elevation of water, because the leaves above fade 

 when these cells are killed by heat. The fading of the leaves in these 

 cases is probably largely due to the introduction of poisonous or 

 plasmolysing substances into the leaves from the dead cells. Clogging 

 due to the exudation of comparatively impermeable substances into the 

 water-conducting tissue of the plant may also contribute to the fading 

 of the leaves. It is further possible that the application of heat in 

 these experiments may permanently interrupt the water supply by 

 breaking the water-columns, on the continuity of which the water 

 supply depends. 



Transpiration of Fouquieria splendens.f — W. A. Cannon gives an 

 account of his study of this plant by the polymeter method (a new 

 method of studying the transpiration of plants in situ, which will 

 shortly be described elsewhere). By this means the transpiration of a 

 plant in the field can be studied many times without injury to it, and 

 observations made on the seasonal as well as on the daily variation. 

 The experiments were begun in February, and continued until after the 

 rains of summer were over, during 1904, a season in which the rainfall 

 was smaller than usual, and the conditions during most of the year very 

 severe. Fouquieria splendens is the ocotiUo of the native Mexicans, and 

 one of the most striking desert shrubs, flourishing in habitats which 

 are so dry as to be unfit for many desert plants. During the dry season 

 the branches are naked, but in the rainy ones are well covered with 

 rosettes of small leaves which are borne in the axils of the spines. 



* Scientif. Proc. Roy. Dublin Soc, xi. (n.s.) pp. 7-12. 



t Bull. Torrey Bot. Club, xxxii. (1905) pp. 3!)7-414 (7 figs, in text). 



