60 Mr. A. Heufrey on the Progress of Physiological Botany : 



developed out of the middle cells of the series, and thus presents 

 two appendages at a certain stage. 



Begonia cucullata offered a very favourable opportunity for the 

 investigation, from the great transparency of the cells of the coats. 

 Here Miiller states that he is certain that the germinal vesicle is 

 formed by a cytoblast in the cavity of the embryo-sac. In Ela- 

 tine alsinoides the coats of the ovule are so much developed that 

 it becomes necessary to make a section of the ovule to see what 

 goes on in the embryo-sac. In this plant again the fertilization 

 was found to occur precisely as in the preceding species — the pro- 

 gress of the phaenomena is here exceedingly rapid. In Epilobium 

 angustifolium the embryo was found to be developed in the same 

 manner, but the author could not trace the pollen-tube to the 

 embryo-sac, a section of the ovule being necessary here also. 



W. Hofmeister* has published an account of a series of obser- 

 vations on the impregnation of the (Enotherece, his examples being 

 Godetia quadrivalvum, G. rubicunda, CEnothera longifiora, (E. Sel- 

 lowii and Boisduvallia concinna. His results are in perfect ac- 

 cordance with those already noticed as to the real operation of 

 the pollen-tube upon the embryo-sac ; he finds that the pollen- 

 tube does push it inwards a little distance in some instances 

 where the embryo-sac is very delicate, in other cases it is itself 

 distorted by the resistance of the embryo-sac. 



The first phsenomenon which presents itself in the embrj'o-sac 

 is an accumulation of the protoplasm at the micropyle end of the 

 embryo-sac, and in this we soon find from two to four free cell- 

 nuclei. Round one of these nuclei (cytoblasts) a cell forms, which 

 is the germinal vesicle ; a second is next produced, which some- 

 times divides into two. From one of these the embryo is deve- 

 loped ; and that this is the case, and that the end of the pollen- 

 tube does not become the embryo, is the more certain, since at the 

 time of fertilization the pollen-tube and embryo-sac are so firm 

 that they may be separated with a needle under the microscope ; 

 the fertilizing matter must therefore pass through three mem- 

 branes, viz. those of the pollen- tube, of the embryo-sac, and of 

 the germinal vesicle itself. 



In Godetia traces of the pollen-tube were found even in the 

 ripe seed, and during the progress of the development of the em- 

 bryo here the pollen-tube branches as it hes in the canal of the 

 inner coat of the ovule, while the cellular layer around the em- 

 bryo-sac has been absorbed, so that the latter with the contained 

 embryo lies free in the ovule. 



* Untersuchungen des Vorgangs bei der Befructung der G^nothercu, von 

 W. Hofmeister. — Botanische Zeitung, Nov. 5, 1847. 



