io6 
Peirce . — The Dissemination and 
of the bark of the Monterey Pine. Until its further growth is opposed by 
some obstacle — a slight elevation of the surface or the base of a bunch of 
leaves or of a branch (Figs. 17, 18, 19, 21) — the root grows on, always 
toward the trunk of the tree. In colour it is usually more or less 
claret-red. 
When the further growth in length is blocked, the root forms a thick 
holdfast. This is shown in Figs. 13, 17, 18, 19, 21. The holdfast consists 
at first of an undifferentiated mass of dividing and growing parenchymatous 
cells covered by a single layer of dermatogen cells which above differentiate 
into ordinary epidermis cells, and below, where the cells are in contact with 
the bark, elongate somewhat and firmly attach the holdfast to the bark, 
much as is the case in Cuscnta (Peirce, 1893) an d other haustoria-forming 
parasites. Into this growing foot the material in the upper (cotyledonary) 
end of the embryo or seedling is transferred. In consequence this upper 
end shrinks as the lower grows, the * seed ’ coats become loosened and may 
blow away, and the seedling becomes mainly a foot with a small and 
shrivelled prolongation (see Figs. 18, 19). In this foot (shown in section in 
Fig. 13) differentiation begins, vascular tissues form, and then the central 
part of the foot grows out into the bark. That both pressure and chemical 
action co-operate in the penetration of the haustorium into the host is highly 
probable, to judge from other cases (Peirce, 1893, 1894), but the effects of 
pressure are far from evident. Instead, appearances all point to the much 
more important action of substances excreted by the cells of the haustorium, 
enzymes which dissolve the walls of opposing cells and hence permit the 
easy and rapid penetration of the haustorium through the dead outer bark 
into the living cortical parenchyma of the host. The haustorium has no 
cap, the cells at the tip elongate and spread out as in Ctiscuta (Peirce, 1894), 
forming strands of infecting-cells which grow in various directions toward 
the medullary rays of the host, grow through these to and through the 
cambium, dissolving the opposing cells as they grow. Finally, the haustorial 
cells effect a direct attachment with the young cells of the wood of the pine 
branch. These last haustorial cells and those above them differentiate into 
tracheids, some of the cross-walls may disappear, and a direct connexion 
by conducting tissue is established between the wood of the host and the 
mass of Arceuthobhim cells in the cortex of the host. 
It is to be noted that, while the cells at the tip of the haustorium are 
growing out and forming infection strands which penetrate the medullary 
rays of the host, the main part of the haustorium is increasing in size, 
forming a mass of parasitic cells in the cortex of the host (Fig. 22). 
Morphologically this mass is a part of the haustorium, itself a special out- 
growth of the tip of the radicle of the seedling. This mass presently 
differentiates into conducting and parenchymatous tissues, buds form which 
develop into branches which grow out through the bark into the air (Figs. 
