ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 137 



epidermal cuticle. 2. The peculiar orientation of the leaves, which 

 appears to serve the purpose of providing the shade necessary for the 

 breathing-roots. The histological examination of the stem shows that 

 there are no true medullary rays, since each ray is restricted in length to 

 the width of each ring ; bauds of vertical walls of sclerenchymatous cells 

 limit the length of the rays. The phloem-cells, which form regular 

 clusters on the outer edge of each ring, appear to be capable of function- 

 ing as ordinary bark. The wood-fibres have a somewhat remarkable 

 distribution, and the wood-parenchyma between them and the stone- 

 cells apparently performs the work of caml;)ium. There is nothing 

 corresponding to the spring and autumn growths found in other 

 dicotyledonous trees, although the annual rings are well-defined ; the 

 greatest peculiarity of the rings is their discontinuity, the break being 

 due to the intrusion of another " ring " in juxta-position but at quite 

 a different angle to the normal ring. The author has given especial 

 attention to these rings, and finds no evidence to support the theory 

 that they are due to forest fires or difference in tides. In his opinion 

 they ai-e due to an endeavour to attain a maximum of strength by a 

 minimum of weight, disposed in fibres or breaks as required by the 

 large amount of foHage borne by the tree ; they may also give strength 

 to resist river-currents and tides. A noticea])le feature of the tree is the 

 impossibility of killing it by ring-barking. This appears to be due to 

 each " ring " being in itself a fascicular bundle, so that destruction of 

 the bark only deprives the tree of a ring of outer cortex, and the 

 numerous remaining phloem-streaks are able to carry on the function of 

 the injured outer portions. 



Reproductive. 



Floral Pedicel of Mesembryanthemum.* — G. Barthelat contributes 

 a short note upon the structure of the floral pedicel of Mesemliryan- 

 themum. The author finds that at least twenty-five species of this 

 genus have fibro-vascular bundles in the cortical tissues of the pedicels. 

 These bundles vary in number and extend to different levels of the 

 floral axis. In some species they form a more or less regular circle in 

 the central parenchyma, and terminate in the lower half of the pedicel 

 without forming any connexion with the chief bundles of the central 

 cylinder ; their orientation is normal. In other species the structure 

 and disposition are analogous, but the bundles extend into the upper 

 portion of the floral axis. All these bundles have the same origin ; they 

 are secondary, descending bundles which arise in the sepals, and, after 

 crossing and anastomosing in the ovary, pass into the pedicel. The 

 number, disposition, and importance of the principal bundles of the 

 central cylinder are in close connexion with the structure of the flower. 



Parthenogenesis, Parthenocarpy, and Phenospermy in Nicotiana.f 

 T. H. Goodspeed has investigated the claim of Mrs. Thomas to have 



* Comptes Rendus, clxiii. (1916) pp. 366-8. 



t Univ. California Publications (Bot.) v. (1915) pp. 249-72 (1 pi.). 



