590 . F. 0. BOWER. 
fertile branch, 7.¢e. anterior and posterior. As to the further 
external characters of the fertile branches I need only refer to 
writings of Hooker, Strasburger, and MacNab. I have nothing 
to add to the detailed account given by Strasburger (‘ Coniferen,’ 
pp. 141, &c.) of the structure of the fertile branches. As he 
describes, the bundles run nearly parallel down them. As they 
enter the main stem of the plant they anastomose with one 
another, and passing inwards, are almost immediately lost in the 
anastomising network of bundles already described beneath the 
surface of the lip. With these bundles they appear to fuse 
(fig. xv). 
‘We thus see that the origin of the male branches is exogenous, 
and since they first appear on the lip of the groove at some 
distance above its base they are adventitious. 
Development of Spicular Celis. 
As before stated, it appears that any cell of the active paren- 
chyma may develop into a spicular cell. It is, however, at the 
lower part of the leaf that the first stages of this process are 
most easily followed, since there the tissues are in a state of 
rapid differentiation from a mass of uniform tissue, such as that 
seen in fig. x. In the mesophyll, which is still actively dividing, 
certain cells cease to divide, increase in size, and put out protru- 
sious in two or more directions. These grow apparently at their 
apex, and push their way between the other tissues at the 
angles where the cells meet (fig. xv). ‘These cells remain singly 
nucleated, and I have never observed a spicular cell with more 
than one nucleus. In spicular cells developing in the stock or 
crown, the growing ends seek out and follow the intercellular 
spaces, where growth is naturally easiest (fig. xvi). As the 
cell increases in size the cell wall becomes differentiated into an 
outer cellulose wall and an inner lignified wall. The well-known 
crystals of calcium oxalate assume, at a very early stage, their 
final development, as may be seen in figs. xvii—xx. They 
are so placed as to remain with one side in contact with the 
cellulose wall, while the other sides are contiguous with the inner 
lignified wall (fig. x1x). That the outer cellulose wall is not 
merely composed of the cellulose walls of the surrounding cells 
(as might be concluded from such a case as that in fig. xx) is 
shown by the existence of it in those parts of the wall of spicular 
cells which abut on intercellular spaces (fig. xvit). The cellu- 
losew all remains permanent. As the cell develops the lignified 
inner wall increases in thickness, till in the fully-formed spicular 
cell the cavity is almost obliterated (fig. xx). This inner ligni- 
fied wall is not uniform. In both longitudinal and transverse 
sections pits are to be seen scattered irregularly between the 
i 
