through Self-adaptation to a Moist or Aquatic Habit. 739 
of cells elongated in its direction and rich in protoplasm. These dissolve 
by disintegration and the tube is formed. The behaviour of the endosperm 
and nucleus is similar to that of Sagittaria variabilis , but this has no 
nucellar tube. 
Mr. Cook refers to Hall as finding resemblances in Limnocharis \ 
Strasburger in Ceratophyllum ; Campbell in Naias and Zannichellia ; all 
being aquatic plants. 
The author calls attention to a probable physiological connexion 
between the tube and the antipodals in Ranunculaceae, Sparganium , and 
Vaillantia, as furnishing nourishment for the embryo. The large lower 
nucleus formed by a division of the endosperm-nucleus (equivalent to the 
nuceliar-tube nucleus) in Sagittaria and Nymphaeaceae showed a resem¬ 
blance which appeared to indicate a similar function, viz. for supplying 
food to the embryo through the agency of the endosperm. In Castalia 
[Nymphaea) this is done by the f core ’ of cells, subsequently by the tube. 
With regard to the embryo, there are the following stages of develop¬ 
ment :— 
1. A globular pro-embryo with or without a suspensor, resembling that 
of Sparganium simplex [and Ranuncidus Ficaria\. 
2. A cotyledonary ‘ ridge nearly circular, enclosing the plumule in 
the middle. N.B.—This ridge is characteristic of Monocotyledons and is 
also present in the pro-embryo of Ranunculus Ficaria , Corydalis cava , Carum 
Bulbocastanum , as also on Tamus and Commelyna. This ridge represents 
the commencement of the usual sheathing base of the cotyledon. 
3. Two cotyledonary lobes are developed from the ridge, giving the 
dicotyledonous character. 
It may be noted that considerable variation occurs. In one , it was so 
great as to give the appearance of two equal cotyledons. [This variety 
appears to indicate the true dicotyledonous origin, but the ridge being not 
quite circular points to partial arrest of one cotyledon.] 
Brassenia and Cabomba differ (a) in having no cell-walls at first in the 
endosperm, (b) the dicotyledonous character appears very rarely. [Hence 
these two genera may indicate the more primitive conditions.] 
The young embryo of Nymphaea advena resembles that of Lysichiton 
Kamtschatense (Aroideae) and of Ceratophyllum. Those of other genera 
are like Sparganium simplex , Naias flexilis and Zannichellia , Potamogeton 
and Lemnocharis , Alisrna , &c. 
Mr. Cook writes elsewhere upon Nymphaeaceae and Sagittaria} 
In certain Nymphaeaceae the endosperm-nucleus divides into an upper 
and a lower nucleus, which become separated by a wall formed across the 
embryo-sac. The upper nucleus forms the endosperm. From the lower 
1 Development of the Embryo-sac in Castalia and Nymphaea. Bull. Torr. Bot., ch. xxix, 
