ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 325 



pairs as first described by Ckristman. While in U. Pom nuclear migra- 

 tion seems to take place only into the fertile cells, in P. Poarum a small 

 number of migrations appear to take place between vegetative hyphse 

 below the layer of fertile cells. The conjugate nuclear condition is thus 

 started before the differentiation of the cells which represent the female 

 cells. This condition leads on to that found in P. Malvacearum, where 

 no aecidium is produced, and the conjugate nuclear condition arises in 

 the vegetative hyphas just before the formation of teleutospores. In 

 Uromyces Scillarum and Puccinia Adoxce there is a further stage of 

 reduction — where the conjugate nuclear condition arises at some un- 

 ascertained stage, but very early in the life-cycle, so that the general 

 mycelium is binucleate. 



Nuclear Division in Hepaticae.* — J. B. Farmer and A. C. Moore 

 continue their controversy about sporogenesis in Pallavicinia, and about 

 the significance attached to the quadripolar spindle by the former writer 

 ten years ago. 



Merbim an, Mabel L. — Nuclear Division in Zygnema. 



Bot. Gazette, xli. (1906) pp. 43-53 (2 pis.). 



Structure and Development. 

 Vegetative. 



Mechanism of the Fall of certain Terminal Buds.f— A. Tison has 

 investigated the mechanism of the fall of certain terminal buds, and 

 finds it exactly similar to that of the autumnal leaf-fall. Most fre- 

 quently only the terminal bud falls, as in Ulmus campestris, Betula 

 alba, etc., but sometimes several terminal internodes also fall, as in 

 Robinia Pseud-acacia, etc. Prior to the full development of the sub- 

 tending leaf, a separating layer is formed just above it, and discolora- 

 tion, extending upwards from this line, is the first sign of the bud's 

 decay. When leaves or leaflets are involved in the fall, each one has 

 its own separating layer. These layers are formed during the plant's 

 maximum period of growth ; their action is slower than that of the 

 layers connected with leaf -fall, since the latter is aided by the weight of 

 the leaf and by frost and thaw. The bud, even when detached, may be 

 held in position by stipules, as in Betula alba. The fall usually takes 

 place in June. The wound caused by the fall is closed in the same 

 way as in leaf -fall. Generally the axillary bud continues the growth 

 of the branch, but in some cases, e.g. Moras alba, this bud dries up 

 (without the formation of a separating layer), and then the one next 

 below continues the growth. The cambium of the growing bud then 

 extends across the base of the fallen bud, thus closing up the central 

 cylinder. 



Reproductive. 



Anatomy of the Flower of the Umbelliferae.} — E. Martel, as a result 

 of the study of the flower, especially as regards the course of the vas- 



* Bot. Gazette, xli. (1906) pp. 67-70. 



T Comptes Rendus, cxlii. (1906) pp. 222-4. 



X Mem. R. Accad. Sci. Torino, ser. 2, lv. (1905) pp. 271-83 (1 pi.). 



