Dr. G. Dickie on the Physiology of Fecundation in Plants. 11 
The position of the exostome in reference to the direction from 
which the pollen-tubes come, presents also a difficulty : Narthe- 
cium is a remarkable instance, and many others must be fami- 
liar to those who have been accustomed to dissect ovaries and 
ovules. 
In certain cases, some ovules, owing to the direction of the ex- 
ostome, are more favourably placed for fecundation than others 
in the same capsule ; for example, in certain species of Spirea, 
Aisculus and others. There are instances in which only one ovule 
reaches maturity, the other or others in the same capsule being 
abortive : a question arises whether this has any connexion with 
the development or non-development of certain parts of the ovule, 
or to the obstacles presented to the action of the pollen ; some re- 
marks on this will be found in the essay of the late Mr. Griffith, 
in reference to Santalum and Osyris, whose embryology he has 
so admirably illustrated. The question respecting the particular 
part of the ovule which sends off a prolongation to meet the de- 
scending pollen-tubes may be left for future consideration ; suffice 
it for the present to say that ovule-tubes do exist in several fami- 
lies ; their presence has been shown in plants belonging to the 
Cucurlitacee, Chenopodiaceae, Polygonacee and Santalacee, and 
to these may be added Juncacee, Scrophularinee and Parnassice, 
probably also in Orchidee. The mode of contact between ovule- 
tubes and pollen-tubes, and the subsequent changes, will also pre- 
sent an interesting field for investigation. The subject is one of 
considerable importance, and it is remarkable that m most phy- 
siological works, even the more recent, no allusion whatever is 
made to it, although Brongniart’s observations were published 
many years ago. ‘There is great reason to suspect that when 
transparent tubes have been seen attached to ovules, they have, 
without further examination, been set down as originating from 
the pollen. 
EXPLANATION OF PLATE I. 
Fig. 1. Fragment of placenta and two ovules of Narthecium some time pre- 
vious to fecundation. 
Fig. 2. Ovule from the same plant about the time of fecundation, showing 
primine, secundine and nucleus with its tube. 
Fig. 3. Secundine and nucleus extracted from the primine. This figure 
must be considered more as a plan made out from several obser- 
vations than an actual representation of the appearance seen in 
any one ovule. 
Fig. 4. A solitary instance in which a distinct funiculus existed. 
Fig. 5. Young embryo and its jointed thread from Habenaria viridis. 
figs. 6 and 7, The same at more advanced periods. 
