260 Dr. Dickie on the Ovule of Euphrasia officinalis. 
For the male to pair with the winged female is a very unusual 
case among Aphides, but it very frequently occurs that genera- 
tions of many families continue viviparous till their final destruc- 
tion, while other families are privileged to carry on the stock of 
the species : their circumstances enable both sexes to appear among 
their descendants, and eggs are consequently laid up in store 
for the ensuing season. But this subject and others in relation 
with it will be more fully noticed in another part of these de- 
scriptions. 
[To be continued.] 
XXV. — On the Ovule of Euphrasia officinalis. By G. Dickie, 
M.D., Lecturer on Botany in the University and King^s Col- 
lege of Aberdeen*. 
In a communication submitted to the Society two years ago, an 
attempt was made to prove that in certain plants, tubes observed 
in connexion with ovules are not really in every case derived 
from the pollen, as stated by some physiologists, but prolonga- 
tions from some part or other of the ovules. This statement had 
reference only to a few plants, and the same restriction is still 
adhered to : it would be rash to generalise in the matter. It was 
argued in favour of this opinion, that the number and position 
of the ovules would present obstacles to the pollen-tubes entering 
their foramina. An argument, it may be said, of greater value 
was employed, viz. that the development of such a tube might be 
traced at an early stage projecting from the exostome in the 
form of a papilla, ending in a blind extremity, afterwards increa- 
sing in length and coming in contact with the placenta. The 
observations of the late Mr. Griffith on Santalum were quoted in 
favour of the idea in question, that acute observer having proved 
the true nature of the tube sent up to meet the pollen-tube, it 
being a prolongation of that part whieh is usually denominated 
embryo-sac. It was not . in my power to speak so emphatically 
regarding the nature of the tubes in those plants in which they 
were seen; in Narthecium, Bartsia and Euphrasia I expressed 
however my belief that they might be prolongations of the apex 
of the nucleus. It was considered sufficient at that time to show 
that prolongations like pollen-tubes might be sent up from the 
ovule. I have repeatedly examined ovules of Euphrasia and have 
found them uniformly present. I had originally set out with the 
view of traeing pollen- tubes into the ovule, and if possible ob- 
serving them in contact with the embryo-sac, and even in the act 
of causing introflexion of that part. When I say, if possible, the 
expression has reference to myself ; observers of great experience 
* Read belorc the Botanical Society of Edinburgh, lo Jan. 1848. 
