
No. 457.] EMBRYO OF THE ANGIOSPERMS. 31 
lier stages of their embryogeny show a great diversity has been 
known for a long time. That this diversity is but the more or 
less restricted following of one general plan has been pointed. 
out by Coulter and Chamberlain (: 032). Up to the present time 
the knowledge of the later stages of their embryogeny has been 
quite insufficient for determining the morphological values of 
the embryonic structures. Recent investigation, however, has 
served to elucidate some of the obscure points, and the interpre- 
tation that would now be offered is as follows. 
In Ginkgo a large spherical protocorm is developed in the 
venter of the archegonium. The blastema (metacormal bud) 
arises as an outgrowth from the deepest seated portion of the 
protocorm and invades the tissue of the gametophyte by its own 
growth. The stem and root primordia are both differentiated 
entirely beyond the bulbous protocorm, the axis of the three 
members being along one straight line (Fig. 8). Upon germi- 
nation, the protocorm 1s the first member to be forced out of 
the seed and it is followed first by the root and then by the 
stem. Thus the protocormal haustrum, because of its position, 
cannot be employed by the metacorm during germination as a 
functioning cotyledon. If any structure is to remain in contact 
with the tissue of the gametophyte, it devolves upon the append- 
ages of the stem, and in Ginkgo we find the first two or three 
euphylls functioning as absorbing organs or pseudocotyledous. 
Ginkgo undoubtedly shows, in its embryogeny, the most primi- 
tive condition of any of the gymnosperms, for it certainly shows 
the least specialization. In Cycas (Fig. 9) a less perfect proto- 
corm is developed and in Zamia (Fig. 10) a further reduction of 
its bulk obtains. In fact it would seem that because of the 
positional relation of the blastema to the protocorm the latter 
cannot be made use of by the germinating embryo, and its dis- 
use leads to an increasing limitation of the structure in gymno- 
spermous embryogeny. | 
In the cycads, protocormal tissue directly behind the blastema, 
by rapid growth, carries the metacormal bud down into the tis- 
sue of the gametophyte (Figs. 9 and 10). This beam he 
suspensor, becomes an organ of importance and is retained by all 
of the Coniferales. Their protocorms, however, consist of little 
