Scrophulariaceae and Orobanchaceae 151 



ical and grow down the sides of the host roots but do not com- 

 pletely surround them. Sections of swellings show an epi- 

 dermis, a cortex, and bundle elements. The most conspicuous 

 feature of the bundles is the large number of cells with pitted 

 walls. The cells in the upper part of the swelling have not fused 

 to any great extent to form vessels, but in the lower spread-out 

 part of the swelling they have the appearance of vessels (with 

 pitted-reticulate thickenings in their walls) which establish a 

 connection with the xylem of the host roots. This was seen in 

 purpurea and pedicularia. 



Roots of Harveya and Hyobanche were not available for inves- 

 tigation. 



Transverse sections of the roots of Lathraea japonica show 

 the epidermis, a narrow cortex, and the polyarch bundle system. 

 In the latter unusually large pitted vessels make up the greater 

 part of the bundles. 



The roots of Aphyllon are soft and delicate, drying quickly 

 when exposed to the air. They never completely surround the 

 host roots, nor do they develop as large swellings as seen in Ger- 

 ardia species when contact is made with the host. The orig- 

 inal root tissues seem to fuse more intimately with the corres- 

 ponding tissues of the host. Root hairs and root caps, as already 

 noted by Smith (18, p. 113), were not found. 



The radial arch-system is maintained, but the bundles are few 

 in number; the small amount of xylem consisting of spiral tra- 

 cheae and pitted vessels is poorly developed. The amount of 

 phloem greatly exceeds that of the xylem, which is a feature we 

 should expect to find in a holoparasitic plant whose chief object 

 of parasitism is elaborated sap. The bundle system is surround- 

 ed by a pericambium and this in turn by a wide cortex of very 

 large cells with abundant quantities of starch. No stone cells 

 have been found in it. Surrounding the cortex is the epidermal 

 layer. So intimate and complete is the connection made with 

 the host roots that, epidermis of parasite is continuous with epi- 

 dermis of host, cortex of parasite with cortex of host, etc., and 

 were it not for the large cells of cortex with abundant contents 

 as compared with the same tissue of the host, the line of demar- 

 cation between the two could scarcely be distinguished. In all 

 this Aphyllon closely simulates species of Orobanche as figured 

 by Koch (19). 



