ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 911 



the stomata, more nearly related to vascular cryptogams than to 

 angiosperms. 



Bordered Pits.* — C. Mikosch thus sums up the results of an in- 

 vestigation of the origin and structure of bordered pits : — 



1. The first clearly differentiated layer in the young wall of a 

 wood-cell is the inner wall ; at the same time, or later, another layer 

 or system of layers arises, constituting the central lamella. Between 

 this and the inner wall is a very watery substance, from which the 

 thickening-layers are subsequently formed. 



2. The origin of the bordered pit is a simple pore, formed in the 

 primary wall. The canal of the pit is developed from the pore by 

 the growth of definite portions of the cell-wall, which proceeds in 

 various ways ; the border, by resorption of certain parts of the 

 division-wall of the pore, which subsequently becomes thicker. The 

 form of the border is determined by that of the thickening of this 

 piece of wall. 



3. The border is clothed on its inner surface either only by the 

 inner walls of adjoining cells, or on one side by the middle layer of 

 the central lamella, which is united with the inner wall ; on the other 

 side, by the inner wall of the adjoining cells alone ; or finally, at the 

 mouth of the pit-canal, the inner walls play the part of lining- 

 membranes, while at the other surfaces the thicker layers of the 

 central lamella do so. 



4. The middle layer of the central lamella may cross the border 

 either in the form of a thin plate, or of one thickened in the middle, 

 and then divides it into two equal halves. 



5. The bordered pit is originally also closed on both sides by the 

 inner wall of adjoining cells ; in some cases, where the above-men- 

 tioned plate divides the border in the middle, a treble enclosure 

 occurs. 



6. When the bordered pit is mature, the closing membranes may 

 either remain (closed pits), or they have partially or entirely dis- 

 appeared (open pits). 



Gum-passages in the Sterculiacese.t — B. Ledig has examined 

 the origin, distribution, and structure of the gum-passages in the fol- 

 lowing species belonging to the Sterculiacese, viz. Astrapcea WalUcMi, 

 Pterospermum acerifolium, Dombeya mollis, Heritiera macrophylla, Bra- 

 chy chiton populneum, acerifolium, and Delabechei, Helicteres involucrata, 

 and Buizia variabilis, and has found a general resemblance to that 

 already described in the allied genus Tilia. They occur chiefly in the 

 pith and cortex of the ultimate branches and of the leaf-stalks. Sterculia 

 Balanghas is distinguished by their entire absence from the leaf-stalk, 

 their place being supplied by laticiferous canals. 



With slight variations in different species, the mature gum-canals 

 of the Sterculiacese have the form of roundish but not sharply defined 

 cavities in the isodiametric parenchyma ; but the neighbouring cells 



* SB. Akad. Wiss. Wien, June 2nd, 1881. See Bot. Ztg., xssix. (1881) 

 p. 466. 



t Bot. Oentralbl., vi. (1881) pp. 387-9. 



