34 COMPARATIVE EMBRYOLOGY OF THE RUBIACEAE 
rants, so that it appears as if the terminal five cells had gone to 
form the embryo proper instead of four. 
The mature ovule consists of a mass of endosperm with cellu- | 
lose as the chief reserve food, and one layer of integumental cells 
still intact. The whole is closely invested by the pericarp. 
The endosperm absorbs the integument till but one or two 
cell layers are left, these forming a membranous lining of the 
pericarp. 
Galium 
p (PLATE 7) 
The species of Galium which have been studied are the follow- 
ing: G. Aparine, recurvum, pilosum, Mollugo, verum, triflorum, 
tinctorum, and Parisiense. As the species of this genus are very 
similar with regard to the characters which we are considering, it 
is not deemed necessary to treat them separately. 
The origin of the nucelli is in all respects as in the forms already 
described, and the same may be said of the number of cells in the 
` archesporium (figs. 1, 2 and 3), their division into megaspores by 
two successive divisions (fig. 4), and the subsequent enlargement of 
one of these to act as the embryo-sac cell. In occasional instances 
two such cells derived from different megaspores may enlarge and 
when germination takes place, two more or less completely formed 
_ embryo-sacs result ( fig. 1I) In one case three such were found, 
although here the third embryo-sac was very abnormal in appear- 
ance. The nucellar epidermal capping cells remain intact until 
the megaspores are fully formed, but suffer histolysis at about the 
time the migration of the embryo-sac mother-cell commences (fig. 
4). The histolysis of the endodermis then follows, as the en- 
larged megaspore moves forward along the micropylar canal. 
The condition of the definitive embryo-sac is reached in the 
usual manner. A two-celled condition is shown in jig. 6. The 
chief interest in this connection attaches to the form the embryo-sac 
takes in the various species of the genus under consideration. The 
various degrees of curvature seen in different species is, no doubt, 
due to the form of the ovule. The more strictly anatropous the 
ovule, the straighter the embryo-sac. In Galium tinctorum in 
which the ovule approaches the campylotrous condition, the em- 
bryo-sac is bent into an arc of ninety degrees ( fig. ro). In other 
