Dr. Dickie on the Ovule of Euphrasia officinalis. 263 



conducting tissue of the style, as in some Crucifera; lastly, 

 tubes proceeding from some part of the ovule itself, as in certain 

 Cupuliferce. Gasparrini alludes to their presence in connexion 

 with the ovule, but supposes them to be derived from the con- 

 ducting tissue of the style ; Hartig and he are therefore agreed 

 in this, in regard to some plants at least. In Orchidea, Amici, 

 Mohl and Miiller have all recently traced the pollen-tube through 

 the foramina of the coats to the embryo-sac. Hoifmeister has 

 made similar observations in the (Enotherea^. Tulasne says he 

 has traced the poUen-tube into the interior of the embryo-sac. 

 The opinions respecting them are therefore three : first, they are 

 true pollen-tubes, an opinion supported by Schleiden, Meyen, 

 Amici, Mohl, Miiller, Gelesnow, Tulasne and others; second, 

 they are derived from the conducting tissue of the ovarium, a 

 view supported by Gasparrini, and also by Hartig, in reference at 

 least to certain plants ; third, they are derived from some part 

 of the ovule itself, issuing from it, not directed towards it ; this 

 opinion derives support from the observations of Griffith and 

 Hartig, and in the first part of this communication I have ex- 

 pressed the same in reference to Euphrasia. 



Admitting that the pollen -tube reaches the embryo-sac f, the 

 opinions respecting their subsequent relation to each other are 

 the following. The view first promulgated by Schleiden was, 

 that the pollen-tube pushed the summit of the embryo-sac before 

 it and became invested by it. Hofimeister admits that the tube 

 in some instances where the embryo-sac is very delicate does push 

 it inwards a little distance, but he also speaks of the tube be- 

 coming distorted by the resistance of the embryo-sac. Gelesnow, 

 and subsequently Tulasne, state that the tube actually penetrates 

 the embryo-sac and lies within it, and Schleiden has recently 

 admitted the possibility of this in certain cases. Amici, Mohl, 

 Miiller and others state that it is merely applied to the sac at or 

 near the apex ; Meyen went a step farther, and supposed that 

 their respective membranes were absorbed at the point of con- 

 tact, thus permitting the direct mixture of the contents of both. 



The action of the pollen in regard to the origin and subsequent 

 development of the embryo may next be alluded to. It may 

 however be observed, that the universality of a law having refer- 

 ence to the necessity for the action of the pollen is not now 

 tenable, after the statement of Mr. Smith respecting the female 

 plant of Ccelehogyne, and the still more recent observations of 

 Gasparrini on the cultivated Fig. These statements will also di- 



* An account of the observations of Amici, Mohl, Miiller and Hoffmeister, 

 by Mr. Henfrey, is published in the ' Annals of Nat. Hist.' for Jan. 1848. 

 t Amici applies the term * embryonal vesicle ' to the earliest stage of this 



