316 MR. A. S. HORNE ON THE STRUCTURE AND 
there may be two synergids, two antipodals, the polar nuclei, and no egg-cell (PL 3E 
figs. 20, 21). Sometimes there is an increase in the number of antipodal nuclei 
(Pl. 31. fig. 24). The antipodals are of the haustorial type described by many authors 
and appear to persist only in sterile ovules. An abnormal number of polar nuclei was 
occasionally observed—in one case as many as seven (Pl. 31. fig. 22). Deceptive 
appearances are sometimes presented in sterile embryo-saes when synergid nuclei with 
three or more nucleoli are found above a single fusion nucleus with a large nucleolus 
derived from unfertilized polar nuclei. Many sterile sacs persist for a long time after 
fertilization time and contain an active antipodal haustorium and occasionally beaked 
synergids: the body of the attenuated sac is occupied by a mass of protoplasm containing 
the large fusion nucleus with very large nucleolus. A similar fusion nucleus is formed 
in sterile sacs of Cornus. In two or three instances there were indications of a 
possible visit of a pollen-tube. There appears to be a single genuine case of 
fertilization where in a normal sac a small nucleus, presumably the male, oceurs in 
juxtaposition to the egg-nucleus. Owing to the degree of sterility of the material, the 
presence of partially destroyed nucellar cells and of embryo-sacs in various stages of 
disintegration, and of multinucleolate nuclei, it is impossible to record anything definite 
about fertilization. In early phases of megaspore development the encroachment upon 
nucellar tissue may extend to the epidermal layer, rupturing it and exposing the young 
embryo-sac. Where there are several developing sacs, the internal limiting layer and its 
subjacent cells of the integument itself may be attacked. There is no recognizable 
“calotte” as there is in 4wcuba. A small, few-celled nucellar cap persists for a time 
after fertilization—this cap being larger in the case of developing sterile ovules. 
The chalazal region or stalk of the nucellus keeps pace with general ovular growth 
by the elongation of its cells. The cell protoplasm becomes highly vacuolate and 
probably serves to conduct the supplies brought by the, as yet, unbranched bundle to 
the chalazal region. The haustorial antipodals penetrate a little among these cells and by 
their absorptive action the embryo-sac receives nourishment. During the development of 
the megasporangium the investing tissue increases in bulk both by cell-division and 
increase in size of the cells, the net result of these processes being a greater proportional 
increase in length over circumference. After fertilization time, the tissues of the congeni- 
tally-fused integument and raphe (extra-nucellar tissue) begin to show differentiation into 
an inner meristematic zone including the internal epidermis and an outer developing 
passive zone. The two tissues, which are at first practically indistinguishable from one 
another, become more and more distinct as the young seed grows. "The expansion of the 
narrow cylinder of meristem, increasing in size mainly by cell-division in transverse OF 
obliquely transverse planes, eorrelated with the passive character of the cortical cells, 
causes continual increase in length over girth during cell enlargement, so that the ovule 
becomes almond-shaped. That the directive force is exerted axially downwards 18 
clearly shown by the fact that previously transverse cortical rows arch downwards 
as if they had been drawn down towards the axial cylinder. The shape of the individual 
cortical cells is, therefore, more or less irregular and attenuated. During growth the 
vascular bundle of the raphe branches considerably, the system remaining just within the 
