Germination of Arceuthobium occidental. 107 
20, 21). These branches are pale green, later they become much greener. 
They at first vegetate and later flower. We have here an instance of 
regeneration without wounding, amputation, or other pathological stimulus. 
The small part of the seedling which penetrates the host forms and 
develops stem and leaves, a small part of one organ — the root — develops 
into a complete plant by forming the missing members. 
Goebel (1900) says, ‘Als Organe “ sui generis” dlirfen wir auch 
betrachten die Haustorien der Parasiten.’ He supports this assertion first 
by saying that in Cuscuta y where the haustoria most closely resemble lateral 
roots, there is no positive proof of their being roots though they arise 
endogenously, and in the second place by the haustoria of the Rhinanthaceae, 
Orobanchaceae, and Balanophoreae, which are certainly not root-like in 
appearance. In Arceuthobium the haustorium almost immediately ceases to 
be root-like in appearance, yet it is plainly a modified root-tip. The same 
is the case in Pharadendron and Vis cum. The single root of the seedling 
grows into the host, and in the tissues of the host the tip becomes a mass of 
cells, at first parenchymatous, later including prosenchymatous cells, and sends 
out strands which penetrate the medullary rays and form a direct connexion 
with the tracheids of the host. The primary haustorium of Arceuthobium 
is evidently the primary root of the seedling ; the succeeding haustoria are 
branches of this primary root. In Cuscuta y on the other hand, the haustoria 
arise in the stem of the parasite from that layer of cells which in other and 
similar stems gives rise to lateral roots. It is not merely the endogenous 
origin of the haustoria of Cuscuta y but their origin from that cell-layer which 
ordinarily gives rise to lateral roots, which causes one to believe them to be 
lateral roots (Peirce, 1893). Similarly the lateral roots and the root-tubercles 
of leguminous plants originate endogenously, but it is only when one sees 
that the root-tubercles originate from the same layer exactly as lateral 
roots, and in their earliest stages are indistinguishable from lateral roots 
except by the presence of the infecting strands of bacteria in the cells, that 
one can believe them to be morphologically the same (Peirce, 1902). When 
one realizes the marvellous plasticity, adaptability, of root, stem, and leaf, 
the idea of organs sui generis becomes unnecessary. 
After the parasite has once formed a foot or holdfast on a pine branch 
the succeeding stages above described are passed through very rapidly. The 
vegetative branches emerge much sooner than one would naturally expect. 
There is very little evidence of pressure being exerted by these branches 
in emerging from the bark, probably because they arise as buds on the outer 
part of the mass of parasitic cells in the cortex and are covered mainly by 
the dead and weathering tissues of the outer bark of the host. Later, 
however, as these branches increase in diameter they plainly push back 
the host cells by which they are surrounded. 
When one compares Figs. 1 and 2 with figures of Viscum and 
