Dr. Dickie on the Ovule of Euphrasia officinalis. 263 
conducting tissue of the style, as in some Cruciferce) 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 OrchidecSy Amici, 
Mohl and Muller have all recently traced the pollen-tube through 
the foramina of the coats to the embryo-sac. Hoffmeister has 
made similar observations in the (Enotherece^. Tulasne says he 
has traced the pollen-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, Midler, 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. Hofi‘meister 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, 
Muller 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, Muller 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 
organ. 
