:U2 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tapetal cells break down and their nuclei float free in the liquid which 

 ribs the cavity of the microsporangium. Two definite male cells are 

 formed within the irregularly elongated pollen-grain. In the macro- 

 sporangium the archesporial cell forms a tapetal cell and a macrospore 

 mother-cell ; the latter gives rise to fqur megaspores, the two upper of 

 which lie side by side, while the two lower stand in vertical series. In 

 the mitosis by which the archesporial cell forms the tapetal cell and the 

 megaspore-mother-cell the number of chromosomes was sixteen, and the: 

 same number was found in other sporophytic cells. In the first division 

 of the megaspore-mother-cell and in the microspore-mother-cell the 

 number is eight. 



The polar nuclei fuse completely before fertilisation. The pollen- 

 tubes were traced to the embryo-sac, but the process of fertilisation was 

 not observed. At the first division of the endosperm-nucleus a wall is 

 formed dividing the sac into an upper and a lower chamber ; in the 

 lower (antipodal) chamber, which is the smaller, the nucleus does not 

 divide, but in the other chamber a large number of free nuclei are formed. 

 The author confirms Wille's statement that a primary root is formed at 

 the base of the embryo, but soon disorganises, and a lateral root which 

 is formed very early is the first functional one. This differs from the 

 account given by Ascherson in the Pjlanzenfamilim, according to which 

 this lateral root is the primary root, its unusual position being due to 

 displacement. 



Development of Macrosporangium of Yucca.* — H. S. Reed gives 

 the results of his study of this phase in the life-history of Y.Jilamentosa* 

 An apical hypodermal cell divides periclinally to form a primary tapetal 

 cell and a sporogenous cell ; the former divides by two anticlinal walls 

 at right angles to each other forming four tapetal cells, closely resembling 

 the reproductive cells in size, contents, and staining qualities. The 

 sporogenous cell forms an axial row of four potential megaspores, fre- 

 quently the walls between the upper two are parallel with the long axis 

 of the ovule, so that there are two megaspores side by side immediately 

 beneath the tapetal cells. Three of the cells of the megaspore-row 

 disintegrate, the one which becomes permanent was in every case 

 apparently the lowest but- one. As it erdarges, the walls of the sister- 

 cells break down and their contents are absorbed, leaving the macrospore 

 in a long pointed cavity in the middle of the nucellus. The germination 

 of the macrospore follows the usual course ; by the time the sexual 

 nuclei are formed the tapetal-cells and part of the nucellus have disin- 

 tegrated, leaving the apical end of the embryo-sac in contact with the 

 epidermis of the macrosporangium. At the basal end a narrow haus- 

 torium is formed, extending through the nucellus nearly to the vascular 

 bundle, the division of the nuclei in the germination of the spore takes 

 place in this tube ; after completion, the egg-cell and synergids move to 

 the apical end of the sac, and the definitive nucleus also moves out, but 

 the antipodal nuclei usually remain in the tube. A mucilaginous 

 secretion is emitted by the columnar epidermal cells of the placenta and 

 the basal part of the funicle a short time before fertilisation. This. 



* Bot. Gaz., xxxv. (1903) pp. 209-14 (5 figs, in text). 



