690 summary of current researches relating to 



nricrosporangial archespore. Its first division is heterotypic, arid 

 corresponds to the first pollen-mother-cell division in every respect. 

 The number of chromosomes in the vegetation nucleus is about 3G ; 

 during the heterotypic and "reducing" divisions, 18 may be counted. 

 The apparent reduction takes place, therefore, prior to the first division 

 of the archespore. 



Potamogeton foliosus. The mature embryo-sac contains two small 

 synergids and a large egg-uucleus near the micropyle enclosed by a 

 wall, a very thin parietal layer of protoplasm, and four antipodal cells 

 cut off by a transverse wall at the lower end of the embryo-sac, of which 

 three are very small and one is very large. The nuclei are peculiar in 

 having most of the chromatin aggregated in a ball at the centre of the 

 cavity. At the time of fertilisation the two sperm-nuclei lie together 

 near the egg-nncleus, but only one is really in contact with it. 



Canna indica. The nuclei of Carina resemble those of Caltha more 

 nearly than those of Potamogeton. They have a true nucleole but no 

 central chromatin mass. The number of chromosomes in the vegetative 

 divisions is six ; when passing to the poles at the heterotypic division 

 there are still six ; but in the second division there are only three. This 

 number is one of the smallest yet found in vegetable tissue. 



In all three species examined the hypodcrmal cell at the apex of the 

 nucellus divides into an upper and a lower cell, of which the inner cell 

 becomes the archespore, and the upper one forms part of the wall of the 

 embryo-sac. 



Endosperm and Embryo of Peperomia.* — Mr. D. S. Johnson does 

 not agree in all respects with the observations of Prof. Campbell on the. 

 structure of the embryo-sac of Peperomia pellucida. But both this 

 species and others of the same genus do present peculiarities not hitherto 

 observed in other families of plants. In the formation of the endosperm, 

 the embryo-sac first of all divides into two by a cell-wall stretching 

 from the oospore to the base of the sac. Two endosperm cells arc 

 thus formed, which subsequently divide into a large number, each with 

 a large nucleus and several nucleoles. There is no group of basal 

 nuclei corresponding to the antipodals, and only a single synergid,, 

 Avhich is long persistent. Finally the endosperm nucleus is formed by 

 the fusion of a large number of small nuclei. 



"O* 



Embryology of Avena fatua.j — Mr. W. A. Cannon has studied the 

 development of the flower and of the embryo in this grass. The gene- 

 rative nucleus divides within the pollen-grain, and the male cells are 

 elongated spindle-shaped ; the archesporial cell of the ovule cuts off no 

 tapete ; the four potential megaspores are formed in various ways. The 

 antipodals multiply before the impregnation of the ovum-cell, becoming 

 36 or more in number, and begin to disorganise with the beginning of 

 the development of the endosperm. The suspensor consists of only a 

 single cell. The cotyledon and the stem-apex are developed from the 

 distal segment of the embryo ; the root, the root-cap, and the periblem 

 initials of the root from the middle segment ; and the coleorhiza from 



"»* 



* Bot. Gazette, xxx. (1900) pp. 1-11 (1 pi.). Cf. this Journal, ante, p. 217. 

 t Proc. California Acad. Sci., iii. (1900) pp. 329-64 (5 pis.). See Bot. Gazette. 

 xxix. (1900) p. 445. Journ. Applied Micr., iii. (1900) pp. 718-9. 



