454 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Gymnosperms is advantageous where photosynthesis is impossible. The 

 division of the second male nucleus in the egg of some Gymnosperms, 

 and its fusion with the segmentation nucleus in Abies balsamea, favours 

 the view that the endosperm of Angiosperms is a modified gametophyte. 

 Extremes in variation in the male gametophyte are found, on the one 

 hand, in Araucaria with 20-44 cells, and, on the other, in Cryptomeria 

 japonica, which not only has no vegetative prothallium, but the wall 

 between the tube nucleus and the primary spermatogenous nucleus is 

 transitory. 



Development of the Pollen-Grain and Anther in Onagraceae.* — 

 E. Beer finds that in the pollen-grains of some Onagraceas the young 

 cell-membranes contain cellulose and pectose, but the sporogenous cell- 

 membranes gradually come to be formed only of pectose. The pollen- 

 mother-cell wall is of pure callose. The first two divisions of the 

 pollen-mother-cell have seven chromosomes, afterwards there are four- 

 teen. The first membrane formed directly by the protoplast is of 

 pectose, deposited upon but distinct from the callose wall. Within this 

 membrane a secondary thickening of pectose is formed. The inter- 

 stitial bodies are special, thin areas on the first pollen-membrane, which 

 are afterwards covered with mucilage ; later on, the latter may give rise 

 to a dense, closing disk, as in- Oenothera, or to lamina?, as in Gaura. 

 Both the first pollen-wall and the secondary thickening layer are 

 attached to the protoplast when first developed, but the greater part of 

 subsequent growth of both membranes takes place by intussusception, 

 after they are completely separated from the protoplast. The material 

 required for their growth is derived from the protoplast, which when 

 nearly exhausted is replenished by the disintegrated nuclear material of 

 the tapetum. If this material is insufficient, further development 

 ceases. The pollen nucleus remains in connection with the interstitial 

 bodies by means of cytoplasmic threads, and just here the intine starts 

 growth. In Gaura Lindheimeri and Epilobium tetragonum the intine 

 contains both pectose and cellulose, but in CEnothera cellulose is almost 

 or entirely absent. The interstitial disk and laminae are eaten away, 

 suggesting the action of an enzyme. The mature pollen-grains are 

 held together by fibrils derived from the mother-cell wall. 



Physiology. 



Nutrition and Growth. 



Ascent of Sap.f — A. Ursprung has experimented with beech stems, 

 and draws the following conclusions as to the part played by the living 

 cells in the ascent of sap. All experiments upon stems, pedicles, etc., 

 tend to show that living cells assist in the production of force for 

 raising the sap, and that the co-operation of the living cells of the 

 wood is necessary for a long time. In older beech twigs, the riving 

 cortical cells have no influence on the sap ascent, and even in the 

 youngest parts their influence cannot be important. For the necessary 

 transmission through the length of one decimetre, only a very small 



* Beih. Bot. Centralbl., xix. Abt. 1 (1906) pp. 286-313 (3 pis.). 

 f Jahrb. wiss. Bot., xlii. (1906) pp. 503-44. 



