412 MISS М. BENSON—CONTRIBUTIONS TO THE 
resist the pressure and become spindle-shaped, and occasionally bi-nucleate, themselves, 
but it is difficult to discriminate between a nucleus breaking down in process of 
degeneration and an active one when the cells are surrounded by a degenerating tissue, 
It is, however, important to bear in mind that small spindle-shaped cells appear around 
the base of the axial strand, and are formed sometimes by divisions arising obliquely in 
this row, and apparently sometimes by secondary modification of members of the 
immediately contiguous lateral strands. They are generally at first smaller than their 
neighbours, although some are destined later to undergo a strikingly new development 
(figs. 16, 17). 
Meanwhile the cell about to become the embryo-sac has enlarged. Its nucleus has 
divided into two and then into four in a manner entirely normal. Later on the 
polar nuclei fuse and form an exceptionally large and conspicuous definitive nucleus 
(figp. 21, d.».) which is connected with other contents of the sac in all directions 
by anastomosing moniliform strands, often of great tenuity. Аз previously described, 
in Fagus this nucleus passes into the cecum, which is now extruded. In Castanea 
the cecum breaks its way through the side-wall of the nucellus near its apex, and 
runs down between the long cylindrical nucellus and the inner integument (fig. 20) 
and very quickly reaches the base of the nucellus. The antipodals are consequently not 
thrust to one side, and they arrange themselves in а tier as shown in fig. 21, а. It is 
around this pointed organic base of the embryo-sac that we first observe the appearance 
of small tracheides, one or more of which ultimately reach a considerable size and 
become remarkably conspicuous objects under the microscope. Ав these at once suggest 
an homology with the tracheides in the sporogenous tissue of Casuarina as figured 
by Treub* in plates xix. and xx., I have given several drawings of them (figs. 21- 
27). Itis by far the commonest result in а longitudinal section to find but one tracheide ; 
indeed fig. 22 represents the only preparation I have obtained that shows a complete and | 
symmetrical arrangement of such tracheides around the antipodal extremity of the embryo- 
sac. Their function is as unaccountable to me as that of the tracheides in Casuarina was 
to Treub; but I do not think we can doubt their homology when we bear in mind the 
undoubtedly sporogenous nature of the tissue surrounding the embryo-sae in Fagus, and 
the great structural resemblance of the nucellus of Castanea to that of Fagus. Moreover, 
they are never found outside the well-marked defeneration-area which extends for a 
short distance down the centre of the nucellus, and they appear to carry on their develop- 
ment even when the embryo-sac, as in many of the abortive ovules, has ceased to expand. 
The whole character of these tracheides is so distinct from that of any other cells in the 
nucellus, whether of Fagus, Quercus, or Castanea, that I have little hesitation in 
regarding them as a vestige of some long-lost. structure. But the strongest evidence 
in support of this claim lies in a comparison of the spindle-shaped cells, and their 
later stages as tracheides, with the long, narrow, pointed cells about to be described in 
the case of Carpinus (Pl. LXXI. fig. 48, s.). We see there the coaxial system of strands 
is almost completely merged in one part of its course into a mass of these long pointed 
cells. The only suggestion of these that we find in Fagus is the tendency of the walls 
* Ann. du Jard, Bot. de Buitenzorg, x. 
