66 



BOTANY 



one another obliquely. As a result of the continued thickening of 



m 



6'"' 



FIG. 70. From the wood of the Pine, 7'i/itts sylvextris. 

 A, Hordered pit in surface view ; B, bordered pit in 

 tiingential section; t, torus; '', transverse section of 

 a tracheid ; m, middle lamella, with gusset, M* ; 

 t, inner peripheral layer, (x Mil.) 



Ki<;. 71. Cells from the endo- 

 sperm of Hr/iUhoiial"-' 

 In Hutu in. >[/. I'its in surface 

 view ; p, closing ineiiilirane ; 

 it, liueleus. (X -40.) 



the cell wall, the canals of several pits often unite, and so BRANCH KD 

 PITS are formed. Such branched pits have usually very narrow 



^ 



Fio. 72. Part of two 



sieve - tuU's of the 

 Pine, I'iiniK xi/l'- 

 showint; sieve - pits. 

 (x 540.) 



A 



KK.. ~X. A, Part of ;in anniil;ir trnrheid ; 

 ]:. ]>art of a s]>ir:d trai-heiil ; C, l"ir^i- 

 tudinal section through |<iirt of a 



retic'iil;ite vessel, showing: the remains 

 of :i partition wall, x. ( 1MH.) 



canals, and occur for the most part only in extremely thick and hard 

 cell walls, as, for instance, in those of the so-called sclerotic cells or 



