694 Sargant.—Recent Work on the Results 
cell, is not by itself conclusive, for there is always the pos¬ 
sibility that the polar fusion may have been retarded in any 
one instance. We require either a large number of such 
preparations to establish a strong probability that one of the 
fusing nuclei is generative, or several instances in which both 
generative nuclei are free in the embryo-sac, each approaching 
its proper goal. For before conjugation the generative nuclei 
can commonly be distinguished from those surrounding them 
by their smaller size and deeper stain. But such preparations 
are exceedingly rare: the passage of the generative nuclei 
from the pollen-tube to the nuclei with which they are to fuse 
must be tolerably rapid, for they are seldom caught on the 
way. Thus it may easily happen that thousands of sections 
must be passed in review, and hundreds carefully examined 
under a high power, before the point in question is finally 
determined. 
Such difficulties may be prohibitive, and hence they greatly 
limit the choice of material. It is not surprising that in some 
cases only negative results have been reached (Merrel on 
Silphium, 31). Rather we may conclude that the number of 
widely-separated species in which double fertilization has 
been observed in so short a time, affords strong evidence that 
the process is general among Angiosperms which show the 
usual structure of the embryo-sac before fertilization. I think 
we are justified in assuming its existence in any such embryo- 
sac as a working hypothesis until we have the opportunity of 
settling the question by direct observation, and that the 
negative evidence must be very strong which should lead us 
to doubt it. 
II. Movement of the Generative Nuclei. 
The elongated and twisted shape of both generative nuclei 
in the embryo-sac of Lilium Mar tag on suggested to the 
original observers the arrest of automatic movements by the 
action of the fixing agent. This led to comparison with the 
newly discovered spermatozoids of Cycas (Ikeno, 25, 26), 
