254 STUDIES IN FOSSIL BOTANY 



On Professor Weiss's view " the vascular strand and the 

 transfusion cells in which it terminates form a special 

 means of .conducting water from the peripheral to the 

 central tissues of the rootlet, a means which is 

 rendered necessary by the development of the middle 

 cortex into an air-conducting tissue or space." 



When the phloem is preserved, it appears to be 



Fig. 103. — Siigmariaficoides. Transverse section of rootlet, showing vascular bundle 

 and part of cortex ; i.c, inner cortex, connected by a parenchymatous bridge with the 

 outer cortex ; /jr, protoxylem ; tr\ tr", tr"', three portions of vascular strands 

 running to outer cortex ; sp. tr. , spiral tracheides of outer cortex ; j>ar. , patch of large- 

 celled parenchyma. X 67. After F. E. Weiss. Hick Collection (Manchester), 75. 



thickest at the side remote from the protoxylem-angle, 

 extending also along the flanks of the xylem, but not 

 round the point (see Fig. 102, pli). It must be 

 remembered, however, that in the state of preservation 

 of these specimens the phloem cannot be distinguished 

 with certainty from peri cycle or from cambium. 



The elements of the wood do not, in the ordinary 

 cases, show any radial arrangement, and are no doubt 

 to be regarded as primary. In exceptional cases, 



