28 THE AMERICAN NATURALIST. |. (Vor. XXXIX. 
viceable as designating the whole embryo before this primary 
differentiation is complete, and the term »zetacorm for the plant 
body after the differentiation of its permanent members. All 
of the protocorm or only a portion of its tissue may be employed 
in the formation of the metacormal primordia. 
In the Bryophyta the haustrum remains embedded in the tis- 
sue of the gametophyte throughout its own existence, but in the 
Pteridophyta it acquires the habit of anchoring the sporophyte 
in the soil after the tissue of the gametophyte is exhausted. 
This seems to have at first resulted in the production of a large, 
bulbous haustrum (Phylloglossum, Lycopodium cernuum) but 
later some haustral tissue became modified into a distinctive 
earth-boring organ, the root, a structure much better adapted 
for penetrating and drawing water from the soil In Zycopo- 
dium cernuum the bulbous haustrum may give rise to roots, 
which in turn may be converted back into bulbous haustra. 
While some lycopods produce large, bulbous, geophilous 
haustra, among the pteridophytes, as a rule, a bulbous haustrum 
is employed only in connection with the gametophyte, the haus- 
tral tissue which penetrates the soil being differentiated into a 
root. Thus the primary bulbous haustrum of the bryophytes 
becomes differentiated in the pteridophytes into two distinct. 
haustral organs; the nursing-foot or cotyledon — the haustrum 
of the protocorm, and the root — the haustrum of the metacorm. 
The capsular sporophore of the Bryophyta gives place in the 
Pteridophyta to an axis bearing sporophylls. Because of their 
position, the photosynthetic work falls upon the sporophylls, 
and this very soon leads to a division of labor with a consequent 
sterilization of some sporophylls as foliage leaves or euphylls. 
While phylogenetically the sporophore precedes the haustrum, 
the requirements of the former during its development upon the 
latter, seems to have stimulated an ontogenetic acceleration of 
the haustrum and a corresponding retardation of the sporophore, 
so that in ontogeny a functional haustrum precedes the sporo- 
phore. Thus in the embryogeny of Anthoceros and Sphagnum 
we find that of the massive protocorms first developed the 
greater portion is haustral tissue on which the sperophore stands 
as a papilla. Among the pteridophytes the ontogenetic acceler- 
