58o 
PHANEROGAMS. 
threads, in which currents are visible, radiate to the walls from the protoplasm 
which envelopes the nucleus. 
[During the growth of the embryo-sac its nucleus divides, and the two new 
nuclei travel to the opposite ends of the sac, a large central vacuole being formed. 
Each of these nuclei divides into two, and each of these again into two, so that there 
are four nuclei at each end of the embryo-sac. One nucleus from each end now 
travels towards the centre of the sac, where they meet and coalesce to form the 
definitive nucleus of the embryo-sac ; these two nuclei may be termed the polar 
nuclei. Round the three nuclei at the two ends of the sac a process of free cell- 
formation now takes place, so that there are three cells at each end of the sac. 
The cells at its lower (chalazal) end soon become surrounded with cell-walls, and 
constitute the antipodal cells : the cells at its upper (micropylar) end remain naked, 
and constitute the egg-apparatus. Two of the cells of the egg-apparatus lie nearer 
the apex of the sac than the third ; they are somewhat elongated superiorly, and 
the nucleus lies in this elongated portion, the rounded inferior portion containing 
a large vacuole : these cells have been termed by Strasburger the Synergidce. In 
many cases the elongated superior ends of these cells presents a longitudinal 
striation (as in Gladiolus, Crocus, Santalu?n, Zea, Polygonum, etc.), first observed by 
Schacht ^ and termed by him the Filiform Apparatus. The third cell, which lies 
at rather a lower level than the other two, is the oosphere : it is more or less rounded 
in form, and its nucleus lies towards its lower end. All three are usually attached to 
the wall of the embryo-sac. It is important to note that the nuclei of the synergidas 
are sister-nuclei; the nucleus of the oosphere is the sister-nucleus of the polar 
nucleus which coalesces with the polar nucleus from the lower end to form the 
definitive nucleus of the embryo-sac. 
The following are some of the principal deviations from the series of pheno- 
mena which have been described above. Sometimes, as in Ornithogalum nutans, 
only one of the synergidse is present. It may be that this is due to the omission of 
one of the divisions of the nuclei at the apex of the embryo-sac; but, inasmuch 
as two are generally to be found in preparations of early stages and only one in 
preparations of later stages of development, it is possible that two are primarily 
formed but that one soon undergoes absorption. In Sinningia, according to Stras- 
burger, only one synergida is present in some cases, and very rarely both are. absent. 
In exceptional instances two oopheres have been found in the embryo-sac, in 
Sinningia by Strasburger, and in Gomphrena by Fischer. This peculiar abnormality 
appears to be the rule in Santalum album. Strasburger explains it by supposing 
either that one of the three nuclei of the egg-apparatus has undergone division, 
so that four cells are formed instead of three, or that the upper polar nucleus 
becomes the nucleus of the second oosphere ; in the latter case, the definitive 
nucleus of the embryo-sac would be constituted by the lower polar nucleus alone. 
The antipodal cells are very imperfectly differentiated in the Orchids, and do not 
become clothed with cell-walls : it is this fact, doubtless, which caused Hofmeister to 
assert that the antipodal cells are frequently wanting in Orchids. In some cases, 
^ Jahrb. für wiss. Bot. I and IV. [Schacht states that in Santalum album the two synergidse are 
separated by a septum which is formed in the apical portion of the embryo-sac ; this observation has 
been confirmed by Strasburger (Zelltheilung und Befruchtung).] 
