LATICIFEEOUS TISSUE OF MANIHOT GLAZIOVII. 197 



By means of these the main trunks of the laticiferous tubes are 

 everywhere connected one with another in the transverse direc- 

 tion. The connection takes place in different ways in the 

 primary and in the secondary phloem. lu the former the lati- 

 ciferous tubes sometimes occur singly, separated by single 

 layers of parenchymatous cells, as seen in tangential section. 

 This is especially the case in the outer regions of the phloem 

 (see fig. 2). In other cases they form bands, each of which 

 consists of two, three, four, or more tubes, and these bands are 

 connected to form a network with long meshes. The indi- 

 vidual tubes forming one of these bands are connected by very 

 numerous perforations of their lateral walls. Tiiese may be so 

 numerous that the greater part of the boundary wall disap- 

 pears, only narrow transverse bands of cellulose being left 

 between the perforations. In other parts of their course tracts 

 of considerable length may be found without any perforations. 

 The single tubes separated by parenchyma, or the constituent 

 tubes of neighbouring bands, are connected in two wavs. 

 Sometimes simple transverse branches extend between the 

 parenchymatous cells from one tube to the other (fig. 2). In 

 other cases complicated anastomosing knots are present, iu 

 which several transverse branches are in contact, and united 

 among themselves by perforations of their horizontal w^alls 

 (fig. 4). 



The laticiferous tubes of the secondary phloem also occur 

 in bands, which are connected to form a network, the meshes 

 of which are occupied by the medullary rays. The tubes of 

 each group are connected among themselves by numerous 

 lateral perforations, as in the primary phloem, and when the 

 bands meet at the top and bottom of a ray their tubes also 

 anastomose, so that open communication, in the tangential 

 direction, exists throughout the entire network. The medul- 

 lary rays of the secondary phloem are not traversed by branches 

 of the laticiferous tubes, so that t!ie frequent transverse con- 

 nections of the primary phloem are absent here. Anastomoses 

 in the radial direction were not observed, eitlier in the primary 

 or secondary phloem. 



VOL. XXIV. — NEW SliR. O 



