BOTANY. 



thin partition, thought that the lenticular cavity was formed by the 

 separation of the walls of the two contiguous cells at that place, and con- 



sequently that they were 

 intercellular. This in- 

 terpretation is still given 

 in some books.* 



31. _ While the 

 bordered pits of the 

 Coniferas are never 

 crowded together, in 

 the cells of some 

 plants they an so 

 numerous as to lie 

 closely side by side 

 (Fig. 17). In such 

 case the first thick- 

 ening of the wall pre- 

 sents itself as a net- 

 work of ridges en- 

 closing elliptical thin 

 places. As the thick- 

 ening advances the 

 ridges increase in 

 height, but at first 

 not in breadth ; later 

 they increase in 

 breadth at the top and 

 overarch the thin 

 areas, much as in the 

 bordered pits of the 

 Coniferge. In this 

 case, however, the 

 opening at the top of 

 the pit is an elongat- 

 ed slit instead of a 

 circle (Fig. 17, A, 

 and C, v). The thin 



Fig. 16. Bordered pits of Pinus sylmttris. A, 

 transverse section of mature wood ; m, central layer 

 of the common wall ; t, a mature pit cut through the 

 middle ; t', the same, but in a thicker part of the sec- 

 tion, the part of the cavity of the pit seen in perspec- 

 tive ; t", a pit cut through below its openings ; S, 

 transverse section through the cambium ; c, cambium ; 

 h, very young w_ood-cells ; t, t, very young bordered 

 pits, seen in section ; C, diagram of sectional and lat- 

 eral views of a young bordered pit ; />, diagram of 

 sectional and lateral views of a mature bordered pit ; 

 E, section of a mature pit, seen in perspective ; F, 

 section of a younger pit seen in perspective. A and 

 B X 800. After Sachs. 



plate separating opposite bordered pits of this kind breaks 



* See Le Maout and Decaisne's " Traite Generate de Botanique," 1868 

 [English edition, 1872] ; Griffith and Henfrey's " Micrographic Die- 



