84 



BOTANY. 



gives rise to a complex branching and anastomosing of the 

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



(2.) Scalar if orm vessels. These are prismatic vessels whose 

 walls 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- 



FIG. 74. 



FIG. 75. 



Fig. 74. Pitted vessels of Aristolochla sip^o, from a longitudinal section of the 

 stem ; the vessel on the right is seen in section, that on the left from without ; a.a, 

 rings, which are remnants of the original transverse partitions ; b, b, sections of the 

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



Fig. 75. Tracheldes of Cyti*us laburnum, from a longitudinal tangential section 

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

 partitions are seen ; the mednlbiry ray is surrounded by tracheldes, which are spi- 

 rally marked and sparingly pitted ; at q, two tracheldes have fused by the breaking 

 of the wall ; ,>,. slightly modified cambium-cells. X 375. After De Bary. 



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

 forms they have fusiform extremities. 



(4.) Traclie'ldes. These consist for the most part of single 

 closed cells, or of elements which closely resemble cells ; 



