594 Murrill.—The Development of the A rchegonium 
It is through the first sperm-nucleus that fertilization is 
accomplished. A short time after its entrance into the egg 
it slips from its cell and moves with accelerated velocity 
towards the egg-nucleus, the latter remaining stationary and 
inactive, but probably exercising chemotactic attraction on 
the sperm-nucleus by reason of its rich proteid contents. 
There is no depression at the apex of the egg-nucleus, nor 
other evidence in it of the approach of the sperm. The 
conjugation-path is a straight line from near the point of 
entrance. Since this point is ordinarily at the side near the 
top of the egg, the sperm-nucleus usually strikes the egg- 
nucleus slightly to one side of its apex; when entrance into 
the egg is effected at the apex, the sperm-nucleus strikes 
the egg-nucleus directly at its apex (Fig. 38). Conjugation 
occasionally occurs at the middle of one side of the egg- 
nucleus, as shown in Fig. 40. The same figure also shows 
the second sperm-nucleus very near the egg-nucleus, but there 
is nothing in this or other preparations of mine to indicate 
that both sperm-nuclei ever unite with the nucleus of the 
egg- 
In Conifers, the sperm-cell is very similar to a pure 
vegetative cell. In the Pteridophytes, the nucleus is con¬ 
densed and elongated, with reduced cytoplasm and active 
cilia. In Phanerogams, the nuclei may be elongated, but 
cytoplasm and cilia are absent. The sperm-cells of Ginkgo 
and the Cycads differ from those of the Conifers in possessing 
a eilia-bearing band which propels the cells from the tip of 
the pollen-tube to the apex of the egg. In the Conifers, the 
pollen-tube penetrates to the egg and the cilia-bearing band 
is unnecessary and absent. 
After the first sperm-nucleus has moved to the egg-nucleus 
the second sperm-nucleus remains for a long time in its 
cytoplasm in the upper part of the egg (Fig. 38), and is then 
gradually absorbed, usually after the other contents of the 
pollen-tube have disappeared. The discovery of a tripolar 
spindle (Fig. 46) in the position commonly occupied by the 
second sperm-nucleus at first led me to believe that, being 
