388 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
(1828), and finally, on the fern prothallus by Naegeli (1844). Unger 
(1834-37) studied these bodies in the mosses (Sphagnum and Mar- 
chantia) and declared his belief that they are not infusoria, but are the 
male fertilizimg cells. At this time also the zoologists of the day 
were making the first detailed studies of the spermatozoa of animals. 
Barry (1844) had seen a spermatozo6n within the egg of the rabbit; 
Leuckart (1849) saw them enter the frogs’ egg, and then, in 1851, 
Bischoff and Allen Thompson proved that fertilization is accomplished 
by the actual entrance of the spermatozo6n into the egg. A no less 
important influence, in stimulating the botanical workers on the 
problem of fertilization, was the magnificent work of Hofmeister, 
on the reproductive structures of the mosses, ferns, and conifers. 
By these splendid researches he had indicated to men of less insight, 
and less comprehensive imagination, just the points in the life cycles 
of plants where the critical phases of the reproductive process are to 
be sought. 
Among the many workers engaged on this problem of fertilization 
in plants in the third quarter of last century there was, in consequence 
of readier exchange of information, an attitude of greater considera- 
tion for the work of other investigators than was found in the two 
preceding decades. ‘There were differences of opinion and interpre- 
tation, to be sure, but there was less of that strenuous cocksureness 
when men saw, or thought they saw, differently from others. The 
mistakes of the brilliant Schleiden were perhaps remembered. Men 
like Hofmeister, Pringsheim, and Strasburger added to and modified 
the interpretations of other workers in the same spirit with which 
they remolded their own immature conclusions. There was a spirit 
of cooperation evident; it became possible for a worker to observe 
and record the fate of a pollen tube in good temper and with calm 
judgment. 
The first steps toward the demonstration of a union of two masses 
of living substance at fertilization resulted from the study of a group 
of plants, the alge, in which sexuality had not been proven or generally 
admitted. It had, however, long before been suggested in the case 
of Spirogyra by Hedwig (1798) and Vaucher (1803). 
The alge were in fact especially advantageous for the study of 
fertilization, since the development and behavior of the reproductive 
organs and cells could, without elaborate preparation, be readily seen 
under the microscope, and often followed through in living material. 
Thus, Thuret, in 1853, for the first time saw the active sperms attached 
to the egg of Fucus, and, in 1854, proved experimentally that only eggs 
to which spermatozoids have had access will germinate. He thus 
demonstrated in this alga the correctness of Unger’s unsubstantiated 
surmise (1837) that the spermatozoids are the male fertilizing cells. 
In Gdogonium, Pringsheim, in 1856 (p. 9), watched the spermatozoid 
