320 SUMMARY OF CURRENT RESEARCHES RELATING TO 



dividing. Four divisions occur before cell-walls arc formed. The pro- 

 embryo consists of tbree tiers of cells, the upper two of fourteen each,, 

 the lower of one cell containing two nuclei. A thick plug of cellulose 

 is formed between tbo cells of the upper tier (rosette-cells) and those of 

 the middle tier (suspensors). The suspensors may separate and several 

 embryos develop from one archegonium. As a general conclusion the 

 Podocarporo are considered to be the nearest living relatives of the 

 Abieteae. 



Vascular Structure of the Flowers of Gnetacese.* — W. C. 

 "Worsdell finds traces of the more primitive structure of the older types 

 of Coniferre and of the Cycads in the floral axes and bracts of some 

 members of Gnetaceas. In the bract of the female inflorescence of 

 Ephedra dietachya a tract of centripetal xylem was seen on the ventral 

 side of the collateral bundle. In the peduncle and axis of tho female 

 cone of Welwitschia the bundles of the central cylinder frequently have 

 an inverted strand attached to their dorsal side, an occurrence previously 

 noted by the author in the peduncle of some Cycadean cones ; the inverted 

 .strand may be fused with the main strand to form a concentric structure 

 of which the phloem is the centre. There were also a number of strands 

 showing a more or less complete concentric structure forming a second 

 vascular cylinder outside the first. The author also suggests that the 

 very small lignified elements frequently found opposite the protoxylem 

 of the bundles of the central cylinder may represent centripetal xylem, 

 although their structuro is rather that of ordinary sclerotic cells. 



Anatomy and Morphology of the Flower of Cruciferse, &c. t — 

 E. Martel gives a comparative account of the floral structure of Cruciferaa, 

 and of representatives of the allied orders Fumariaceae and Cappari- 

 daceae. The paper is accompanied by numerous figures illustrating the 

 arrangement of the bundles supplying the members of the various floral 

 whorls. 



Development of Pollinium and Sperm-Cells in Asclepias Cor- 

 nuti.+ — C. S. Gager claims to have settled the question of tho identity 

 of the pollen-grain and its ontogeuy in Asclejrias. The individual cells 

 of the pollinium are true pollen-grains which never become free. Nu- 

 merical reduction of the chromosomes takes place in the primary pol- 

 linium cell, the divisions of which are successive, giving rise to a row of 

 four pollen-grains radially arranged. This arrangement of the individual 

 grains is the chief peculiarity in the division. Otherwise the whole 

 course of development is precisely what occurs in other plants that form 

 pollen-grains. The outer membrane of each pollen-grain is composed 

 of the wall of the mother-cell, which docs not dissolve, plus the cross- 

 walls formed by the two divisions of the mother-cells. In addition each 

 grain has an inner membraue which it develops about itself. 



The generative cell divides, before the formation of tho pollen-tube, 

 into two sperm-cells, each of which travels down the pollen-tube, passing 

 the vegetative nucleus on the way. 



* Ann. Bot., xv. (1901) pp. 766-72 (1 fig.)- 



+ Mem. R. Accad. Sci. Turin, ser. 2, t. li. (1S02) pp. 241-66 (3 pis.). 



X Ann. Hot., xvi. (1902) pp. 123-18 (1 pi.). Cf. this Journal, 1902, p. 199. 



