734 SUMMARY OF CURRENT RESEARCHES RELATING TO 



destroyed larger cotyledon occurs, but the smaller seed-leaf is stimulated 

 to a stronger development and the formation of secondary growth ; new 

 foliage-leaves are also formed. 



In Monophylkm a regeneration of the larger cotyledons occurs only 

 when its basal meristem is intact. If this is also removed the plant perishes, 

 the smaller seed-leaf being unable to take on the function of the larger. 



Rudolph, Karl — Beitrag zur Kenntnis der Stachelbildung bei Cactaceen. (On 

 formation of spines in Gactaceae.) 



[The spines in Opuntia missouriensis are epidermal outgrowths, and not 

 homologous with leaves or branches.] 



Oesterr. Bot. Zeitschr., liii. (1903) pp. 105-9 (1 pi.}. 



(Jhifflot, J. — Sur la symmetric bilaterale des radicelles de Pontederia crassipes 

 Mart. (On the bilateral symmetry of the rootlets of Pontederia crassipes Mart.) 



Comptes Rendus, cxxxvi. (1903) pp. 1701-3 



Reproductive. 



G-ametophytes and Embryo of Taxodium.* — W. C. Coker finds 

 that the staminate cones begin to develop in September or October, and 

 by winter the pollen-mother-cells are formed. Development is resumed 

 in spring. The reducing divisions in the' pollen-mother-cells resemble 

 those in Larix, and the reduced number of chromosomes is probably 

 twelve. There is a resting stage after the first division in the mother- 

 cells. About ten days after the reducing division a generative cell 

 becomes separated from the tube-cell ; no sterile prothallial cells are 

 formed. The generative cell divides into central cell and stalk-cell 

 from two to three weeks after pollination, when the tube has grown some 

 distance. The tube reaches the prothallium earlier than in any case 

 previously described, sometimes even before the formation of a cellular 

 tissue in the latter. The arrangement of the nuclei in the pollen-tube 

 is the same as in other Conifers. The central cell, which has a distinct 

 membrane, divides, simultaneously with the division in the central cell 

 of the archegonium, to form the two sperm-cells. 



The ovulate cones also begin their development in autumn and 

 continue growth through the winter. At the time of pollination the 

 single megaspore mother-cell may be distinguished ; it is filled with 

 starch, as are also the surrounding tapetal cells. Two reducing divisions 

 occur, but only three cells are formed — the upper of the two first 

 produced not dividing again. The lower of the two potential mega- 

 spores, resulting from the second division in the lower cell, develops 

 into the female gametophyte, the two upper cells disorganising. The 

 archegoma are arranged as in the Cnpresseae ; the number of the 

 neck-cells varies from two to sixteen or more. The central cell is 

 very long and contains two conspicuous kinoplasmic areas, one at the 

 upper end near the nucleus and the other in the lower end beneath the 

 large central vacuole. When the ventral canal nucleus is cut off the 

 upper of these masses takes part in the division, while the fragmented 

 lower one fills the base of the archegonium with peculiar figures. A 

 ventral canal nucleus is cut off just before fertilisation, but is not 

 separated from the cytoplasm of the egg, and after fertilisation moves 

 back towards the centre and divides amitotically ; this probably assists 

 in nourishing the embryo. 



* Bot. Gazette, xxxvi. (1903) pp. 114-33 (11 pis.). 



