ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 1009 



Brachysclereids or Braclieids, the star-shaped ophiure-cclls Astro- 

 sclereids, the bone-shaped sclereids of Halcea Osteosclereids. He re- 

 gards all these varieties as specially adapted for mechanical support 

 of the surrounding tissues. 



The osteosclereids, which have often broad and palmately 

 branched ends, are particularly well developed in the leaves of Makea, 

 and are especially adapted to prevent the contraction of the leaves from 

 drying up in hot weather ; their form varies considerably in different 

 species. They occur in several species of Hahea ; also in Protea, 

 llhopala, Stenocarpus, Isopogon, Bestio, Kingia, &c. Of the same 

 nature are possibly the " spicular cells " of XVelmtsehia. 



Bracheids occur especially in the testa of seeds ; offering a firm 

 resistance to external pressure on the one side and to the drying up of 

 the seed on the other side. But their widest distribution is in the 

 bark ; and their function is well seen by comparing the structure of 

 weeping varieties of trees, such as the ash, with the normal ; in the 

 former the stereids are much less numerous, and the bracheids which 

 ordinarily accompany them almost entirely wanting. The same is 

 the case also with many climbing plants, such as Ampelopsis, Hedera, 

 and Celastrus scandens. 



Another function of bracheids is to promote the flexibility of 

 branches ; this is the purpose of the sclerenchymatous layer of the 

 resin-canals of many Coniferje, and of those which occur so abundantly 

 in the bark of young twigs, where they commonly take the form of 

 tangential bands of bracheids between groups of stereids, forming 

 what the author calls a " mixed ring." 



Astrosclereids occur in the leaves of Camellia, and in the bark of 

 Camellia, Magnolia, Abies pectinata, Ostrya, &c, branching greatly and 

 often dove-tailing among the surrounding parenchyma-cells. 



Cambium of the Medullary Kays.* — As the result of observations 

 on the wood of a number of trees, Herr A. Wieler has determined 

 that the cambium of the medullary rays is similar in its character to 

 that of the wood, and persists also during the period of repose in 

 growth ; it therefore cannot be a secondary mer intern. 



Dr. G. Haberlandt, ] however, contests this statement in tho 

 case of Cytisus Laburnum and a number of other trees and shrubs. 



Closing of the Sear after the Fall of the Leaf. J — Dr. L. Staby 

 has investigated the phenomena connected with this process in Dico- 

 tyledons, Monocotyledons, Gymnospcrms, and Vascular Cryptogams. 

 In the latter class no proper healing-tissue is formed. In the three 

 other classes the process is the same in its general features, and 

 provision is made to prevent the degeneration of the cells proceeding 

 far from the locality of the wound, by the cuticularization of the 

 walls of the adjoining cells, and the stopping of the fibrovascular 

 bundles by gum, or by the isolation of the injured tissue by the 



* Ber. Dentech. Bot. Gesell., iv. (1886) pp. 73-7 (2 figs.), 

 t Ibid., pp. 144-50 (1 pi.). 



\ Flora, lxix. (1886) pp. 113-24, 137-43, 155-60 (1 pi.). Of. this Journal, 

 ante, p. 474. 



Ser. 2.— Vol. VI. 3 u 



