50 Mr. A. Henfrey on the Progress of Physiological Botany: 



which pre-exists and is visible in the nucleus before the intro- 

 duction of the pollen-tubes into the ovules. Probably the im- 

 pregnation is effected by the passage of the fertilizing fluid 

 through the membrane of the embryonal vesicle, this fluid being 

 conducted to or deposited in the vicinity, or even on the surface 

 of the latter. It is certain that the vesicle only acquires the 

 power of development after the pollen-tubes have penetrated 

 the coats of the ovule, and poured out the fluid which they con- 

 tain upon it j it dies without having shown any signs of growth 

 when it is not moistened by the fertilizing fluid. 



The subsequent development of the embryonal vesicle shows 

 itself first towards the base ; that is, at the point opposite to where 

 the pollen-tube acts. All trace of this tube has disappeared by 

 the time the enlarged embryonal vesicle begins to multiply its 

 cells j these become enlarged, particularly toward the base of the 

 nucleus, finally reaching its walls, thus entirely filling its cavity, 

 and even causing its rupture. The form which the embryonal 

 vesicle ulteriorly assumes in the course of development is that of 

 a constricted sac (the embryo-sac), within which, at the summit, 

 many days after the epoch of fertilization, a greenish body makes 

 its appearance, which is the true embryo of the new plant. 



From these facts, which are constant, it follows that the pollen- 

 tube is not transformed into the embryonal vesicle*, because the 

 latter exists already in the unfecundated ovule : still less is the 

 pollen-tube developed into the embryo, for the embryo is not 

 produced till long after, when the vesicle, very much enlarged, 

 has become the embryo-sac. Moreover, the embryo is visible 

 long before its diameter is equal to that of a pollen-tube, so that 

 this latter cannot have become converted into it. 



"In reference to CucurbitaPepo therefore,'^ saysAmici," I could 

 be certain that Schleiden^s theory was incorrect, and, microscope 

 in hand, offer direct demonstration. Analogy led me to believe 

 that in other plants, where the action of pollen is necessary to 

 fecundation, the opinion of the German botanist was inadmissible; 

 and I was the more strengthened in this conclusion, that in my 

 numerous earlier researches in other plants, I had never seen the 

 pollen-tube either lodge itself in the embryonal vesicle when the 

 latter existed before fertilization, or itself become the embryonal 

 vesicle." 



After stating that although he had not extended his observa- 

 tions to the families Orchidacece and AsclepiadacecB, he was induced 



not be confounded with the germinal vesicle, which is the first cell of the 

 embryo. — Rep, 



* There is some confusion in the translations here : in the French this is 

 given vesicule emhryonnaire ; but Prof. Mohl uses the term Keimhlaschen 

 (germinal vesicle), with the synonym vesichetta germinativa. — Rep. 



