226 Mr. H. Giraud on the recent Doctrines 



to this observer*, at a very early period of the development of 

 the ovule, a cellule from the interior of the nucleus, which ori- 

 ginally differed not from the surrounding ones, is developed to 

 an extraordinary degree, and presses more or leps on the sur- 

 rounding tissue of the nucleus, which is then absorbed from 

 within outwards. This cellule is the embryo-sac (membrana 

 amnii, Malpighi ; sac-embryonnaire, Brongniart ; quintine, 

 Mirbel) w^hich exists in all phanerogamic plants without ex- 

 ception, even before impregnation. This embryo-sac contains 

 a substance which is gradually transformed into cellular tis- 

 sue ; and being ultimately developed wdthin the embryo-sac, 

 forms (when not absorbed by the growth of the embryo) the 

 endosperm, or albumen of most authors. The pollen tube, 

 having made its way through the conducting tissue of the 

 stigma, and having reached the ovule, penetrates the aperture 

 in the teguments, traverses the summit of the nucleus, and 

 following the intercellular passages arrives at the embryo-sac. 

 Having reached this point the pollen tube presses before it 

 the membrane of the embrj^o-sac, which is then folded all 

 around it ; so that the extremity of the pollen tube appears to 

 penetrate into the sac ; though in reality it is on the outside 

 of it. (PI. IV. fig. 1. and 2.) Thus inclosed the extremity of 

 the pollen tube enlarges into the form of an oval spheroid, and 

 its contents are converted into cellular tissue ; at its sides are 

 formed the lateral organs or cotyledons, from which the ex- 

 tremity remains distinct and is developed into the plumule. 

 The portion of the tube situated above the embryo, and which 

 is embraced by a duplicature of the embryo-sac, is gradually 

 but completely obliterated ; so that the embryo is then left 

 free within its sac. In this way the embryo is formed of two 

 membranes ; — the indented embryo-sac and the membrane of 

 the pollen tube. (Fig. 2.) With these statements of Schlei- 

 den the still more recent observations of Wydlerf agree, 

 exceptas regards the folding in of the embryo-sac, which this 

 last observer has never met with ; but it appeared to him 



* Schleiden, Sur la formation de I'ovule, et I'origine de I'embryon dans 

 les Phanerogames, Ann. des Scien. Nat. 2nde Serie. Botan. Mars, 1839. 



f Wydler, Note sur la formation de I'embryon (Extrait d'une lettre de 

 M. Wydler, professeur k Berne, communique par M. A. St. Hilaire a I'Aca- 

 demie des Sciences k Paris, Oct. 1838.) 



