414 Boeunrg on the Histology and 
Subsequent growth causes elongation of all epidermal 
cells, so that in older portions these sister cells no longer 
project above the surface. After spreading out, the stomatic 
cells flatten somewhat and lay down thickening on their 
outer face. This thickening assumes a slanting position 
(Fig. 12, d). The separation of the two stomatic guard 
cells, especially at their more internal portion, their further 
flattening and increased thickening of the upper wall, com- 
plete the formation of the stoma. Young stomata, even 
when completely formed, have no intercellular space beneath 
them. It is not at all unusual to find two or three stomata 
in a row, but they are always separated by two cells—the 
sister cells just described. Laterally consecutive cells do not 
form stomata. They are strictly in rows. The furrowing 
of these rows is not evident in young stems, and is a sec- 
ondary development, apparently due to the greater expansion 
of parts not in line. This is further borne out by the hol- 
lowed appearance of the furrows. The cells do not sink 
abruptly, but are merely concave. 
As will be seen from the highly organized stem system, 
this plant, while a typical parasite in many respects, cannot 
be said to have been much degraded in its stem histology. 
The extensive xylem system of the stem and branches, and 
its high organization of elements, as well as the abundant 
stomata and large amount of chlorophyll, indicate that the 
plant absorbs crude sap from its host and does much of its 
own elaborating. This position is further fortified by the 
structure of the haustoria, which show well-developed and 
abundant spiral tracheae running into their very ends, which 
curve directly into the wood area of the host. 
That the chlorophyll is very active is shown by the super- 
abundance of starch in the cells wherever chlorophyll exists. 
The hard bast is a good source of support to a plant whose 
stems reach several meters in length, and which, owing to 
its trailing habit and mode of twisting into ropes, must 
often have considerable weight to support. 
