26 



BOTANY. 



tMn partition, thoujrlit 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 

 Coniferse are nsTer 

 crowded together, in 

 the cells of some 

 plants they are 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 tlie 

 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 

 iiS;?fhr™gh7h1 Coniferse. In this, 

 case, however, the 







Fig. 16.— Bordered pits of Firms 

 trariBverse sectioD of mature wood ; 

 of the common wail ; t, a mature r " 

 middle ; t/^ the same, but in a thicker part of the sec- 

 tion, the part of the cavity of tne pit Been in perspec- 

 tive ; t", a pit cut thr.iugh below its openings; B, nr\m\\r\cr n(- thp ^rcn nf 

 transverse section through the cambium; ccamfcium; opening at me lOp 01 

 lells 



h, very young wood-cells; L t very young bordered Y\\c^ "nil !« nn plnno-pf- 

 pits, seen in lection ; (7, diWm of SMtioSal and lat- ^^^ P|^ ^f ^^ ClOngat- 

 eral views of a s'oung bordered pit; Z>, diagram of gd slit instead of a 



sectional and lateral views of a mature bordered pit ; . 



M, section of a mature pit, seen in perspective; F, Circle (ilg. li, 



section of a younger pit seen in perspecttve. * """ ^ ° 



B X 800.— After Sachs. 



and C, c). The thin 

 plate separating opposite bordered pits of this kind breaks- 



* See Le Miinut and Decaisntt's " Traite Generale de Botanique," 1868- 

 [English edition, 1872]; Uriffith and Heufrey's " Micrographic Die- 



