2G2 Dr. Dickie on the Ovule of Euphrasia officinalis. 



and continuous with its neck, is merely a process of that part.^ 

 In Euphrasia, however, the embi-yo-sac does not appear exter- 

 nally, as in the advanced stages of that of Veronica. 



The tube already described as traversing the bulb and neck of 

 the sac, and passing some way into the interior of the body of the 

 same organ, is certainly not the least remarkable part of the ar- 

 rangement. The principal argument against its origin from the 

 pollen has been already alluded to, viz. its closed papilliform end 

 projecting from the fissure in the extremity of the bulb. It is 

 certainly very difficult to pronounce a decision respecting the 

 nature of the extremity of a transparent membranous tube less 

 than a three-thousandth of an inch in diameter. I have come to 

 the conclusion mentioned, after repeated careful examination 

 under various powers of a microscope (by Brunner of Paris) va- 

 rying from 250 to upwards of 600 diameters. Figure 1 repre- 

 sents a preparation in my possession, in which two tubes are 

 lying beside each other ; one of them is evidently broken across, 

 the other is closed at the end ; the latter may be traced to the 

 exostome of an ovule, part of which only is represented. The 

 ruptured tube belonged to another ovule which is not represented 

 in the figure. But for the fact just mentioned, I should feel con- 

 strained at once to admit, that appearances are much in favour 

 of Schleideu's opinion, excepting that part which has reference 

 to the introflexion of the embryo-sac. 



It will now be evident, therefore, that in Euphrasia, the ovule 

 tubes are not prolongations of the apex of the nucleus, but pro- 

 ceed from the interior of the embryo-sac. As already mentioned, 

 I am not at present prepared to state positively the relation be- 

 tween the tube and the embryo. 



The majority of observers seem to agree respecting the pre- 

 sence of pollen-tubes in the tissue of the stigma and style ; and 

 they have been traced into the interior of the ovarium. That 

 part of the subject which has reference to the presence of such 

 tubes connected with the ovule, and their nature, has given rise to 

 much difference of opinion. 



Mirbel long ago pointed out the existence of tubular prolon- 

 gations proceeding from some part of the ovule. Those observed 

 by Mr. Brown in the OrchidecB were supposed to have their exist- 

 ence determined by the action of the pollen, but not to be directly 

 derived from it. Schleiden spoke emphatically respecting the 

 pollen-tubes reaching the embryo-sac, and the same was admitted 

 by Meyen, though they difiiered respecting the subsequent rela- 

 tions of the two. Griffith demonstrated the presence of both 

 pollen- and ovule-tubes. Hartig admitted the existence of three 

 kinds in connexion with the ovules in different plants : first, true 

 pollen-tubes, as in the Conifera ; second, prolongations of the 



