DEVELOPMENT OF THE POLLEN TUBE AND PROTHALLUS. 29 
and figured the pollen tube and prothallus in an early stage still show- 
ing the two prothallial cells in position. In describing the further 
development, however, he says: 
It is thus shown that in the second half of September the first of the two prothal- 
lial cells divides into a body cell and a stalk cell, while the outer prothallial cell 
usually remains undivided. The body cell corresponds to the central cell of an 
antheridium; it increases in size more than double, and its nucleus is enlarged in the 
same proportion. Hereupon this central cell undergoes commonly a cross or oblique 
division, by means of which two generative cells are created. The stalk cell of the 
antheridium is divided apparently only under certain conditions. Then the stalk 
cell and the first prothallial cell lose their independence, and the liberated generative 
cell passes into the pollen tube.' 
This method of development would make Ginkgo correspond nicely 
with what occurs in some of the Conifere, but would seem to be 
quite different from what actually occurs in Ginkgo. 
The writer’s investigation of Ginkgo, so far as carried out, indicates 
that the development of the prothallus here corresponds entirely with 
that described above in Zamza. Shortly after germination the first 
and second prothallial cells can be discovered in the process of exten- 
sion, the first protruding considerably into the second. In Ginkgo the 
writer has not been fortunate enough to find the division of the second 
prothallial cell, which gives rise to the stalk cell and central cell. The 
three-celled stage immediately following the division, however, com- 
pares almost exactly with the three-celled stage of Zamia (compare 
figs. 15 and 18), showing the first prothallial cell protruding into the 
stalk cell, and almost entirely surrounded by it. In older stages, both 
in Ginkgo and Zamia, when the central cell approaches the time for 
division, the first prothallial cell is almost invariably found to have 
grown up within the stalk cell to such an extent that it comes in con- 
tact with the central cell (fig. 20). In Zamia several instances have 
been observed where it has even caused a decided indentation in the 
central cell (fig. 22). Another feature of importance in showing that 
what the writer calls the first prothallial cell is a genuine cell and not 
simply a central portion of a cell inclosed by protoplasmic strands is 
shown in the fact that, in some cells as a result of fixation or a differ- 
ent stage of development, the plasma membranes or //autschichts of the 
two adjoining cells separate, so that one can clearly distinguish two dis- 
1So zeigt es sich denn, dass in der zweiten Hilite des Septembers die vordere 
der beiden Prothalliumzellen in eine Korperzelle und eine Stielzelle zerfallt, wihrend 
die aussere Prothalliumzelle gewohnlich ungetheilt bleibt. Die Korperzelle ent- 
spricht der Centralzelle eines Antheridiums, sie schwillt zum mehr als Doppelten 
noch an, und in demselben Maasse vergrossert sich ihr Zellkern. Hieraut erfihrt 
diese Centralzelle schon vielfach eine quere oder schrige Theilung, wodurch zwei 
generative Zellen geschaffen werden. Die Stielzelle des antheridiums scheint sich 
nur unter Umstinden zu theilen. Dann geben Stielzelle und erste Prothalliumzelle 
ihre Selbstaindigkeit auf, und die befreite generative Zelle wandert in den Pollensch- 
lauch ein. (109, p. 18). 
