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 Spircea, 

 jEsculus 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 

 CucurbitacecB, Chenopodiacece, Polygonacece and SantalacecE, and 

 to these may be added JuncacecBy Scrophularinece and Parnassiece, 

 probably also in Orchidece. 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 in 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. \. Fragment of placenta and two oyvi^esoi 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. 



