260 Dr. Dickie on the Ovule r^/ 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 

 favoiu' 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 which 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 tracing 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 before the Botanical Society of Edinburgh, 13 Jan. 1848. 



