A ctinostrobus pyramidalis, Miq . 333 
in Fig. 28. The nucleus of the body cell has increased in size, and its 
appearance is that of a nucleus about to prepare for division. The cyto- 
plasm is dense and very homogeneous, and the wall is more distinct than in 
earlier stages. This is the structure of the pollen-tube shortly after wall 
formation is complete, and Figs. 29 (a transverse section of the pollen-tube 
and adjacent tissues) and 10 show that it is completely embedded in the 
tissue of the prothallus, and not lying, as is often the case in Widdringtonia , 
between the megaspore membrane and the prothallial cells. It is quite 
possible, however, that it does sometimes lie on the outside of the 
prothallus. 
Since some collections included pollen-tubes both before and after 
division of the body cell, efforts were made to secure stages of this division, 
but entirely without success, although every stage in the rounding off of the 
male cells has been seen in numerous preparations, and many others show 
a body cell like that of Fig. 28. It is, of course, impossible to state pre- 
cisely the period elapsing between the various stages seen of the rounding 
off of the male cells, but the short time which elapses between their formation 
and the occurrence of fertilization makes it likely that these would differ, 
in time, by only a very few hours. Other investigators have evidently 
also had difficulty in securing this division, it having only been recorded 
in comparatively few genera, the latest of these being Juniperus communis , 
var. depressa ) where Nichols (17) figures a few stages of the division, but 
confesses to failure in the endeavour to obtain a complete series. As he 
gives a rhumd of the work previously done on the same division in other 
genera, it is not necessary to say more on that score, but taking into con- 
sideration the various researches of recent years, and the fact that all 
investigators collect at short intervals round about the time of fertilization, 
shortly before which the body cell divides, the conclusion seems inevitable 
that the body cell much more frequently divides at an hour (doubtless in 
the night) when collections are seldom or never made, than at any other 
time. The alternative view would be that the whole division is passed 
through in an exceedingly short space of time. 
As first seen after their formation (Fig. 30) the two male cells appear 
to be still enclosed in the mother-cell wall. This is a stage which has 
apparently not been noted previously, it having been assumed that the 
male cells are not formed within a mother-cell wall. Coulter (4), however, 
remarked in this connexion, ‘ it is not an unreasonable expectation that 
some of the male cells may be found to be formed within mother-cells.’ 
No trace of the mother-cell wall can be seen at a slightly later stage. 
Whether the body cell moves down at about the time of its division, 
or whether the sterile nuclei move up, cannot be positively determined, but 
from the fact that the end of the pollen-tube is some way below the male 
cells, the second alternative seems probable. In any event, the two sterile 
A a 
