84 



BOTANY. 



gives rise to a complex branching and anastomosing of the 

 spirals (Fig. 72, v'""). 



(2.) Scalariform vessels. These are prismatic vessels whose 

 Trails are thickened in such a way as to form transverse 

 ridges, as described in paragraph 32, page 28. They are wide 

 in transverse diameter and their extremities are fusiform or 

 truncate (Fig. 73). 



(3.) Pitted Vessels. The walls of 

 these vessels are thickened in such a 

 way as to give rise to pits and dots, 

 as described in paragraph 31, page 

 26. The vessels are usually of wide 

 diameter; in some forms they are 

 crossed at frequent intervals by per- 



nio. 74. 



Fig. 75. 



Fig. 74. —Pitted vessels of AHstolochia sip'io, from a longitudinal section of the 

 stem ; tiie vessel on ihe liglit is seen in section, tliat on thi' left from without ; a.a, 

 rings, whicii are remnants of tlie original transverse partitions ; 6, 6, sections of tiie 

 walls \ between the vessels are parenchyma-cells, highly magnified. — After Duchartre. 



Fig. 75. — Tracheldes of Cij/uus laburnum, from a longitudinal tangential section 

 of the stem ; m, m, a cross-section of a medullary ray : in ihree of the cells the pitted 

 partitions are seen ; the medullnry ray is sm-roundea by tracheldes, which are spi- 

 rally marked and sparingly pitted ; at a, two tracheides have fused by the breaking 

 of the wall ; s, e, slightly modified cainbmm-cells. X 375.— After De Bary. 



forated horizontal or inclined septa (Fig. 74) ; in other 

 forms they have fusiform extremities. 



(4.) Tracheldes. These consist for the most part of single 

 closed cells, or of elements which closely resemble cells ; 



