72 THE NATURAL UISTOIIY liEVIEW. 



hybiidized by its congeners. F. plati/carpus and F. ceranoldes 

 exhibit the same variability. 



M. Thuret remarks, that he finds nothing to support the supposi- 

 tion of those observers who believe that the spermatozoa eftect an 

 entrance into the spore : he has always seen them on the surface, 

 never within the substance of the spore.* 



AVe have next to consider the division of the Chlorosperme?e or 

 Zoosporeae, in which very important results have been arrived at, 

 principally from the observations of Dr. Pringsheim. 



The plant upon which some of his earliest observations were made, 

 was the well-known Vauclieria sessilis,^ which from the simplicity 

 of its structure offers peculiar facilities for observations of this 

 nature. From the tubular filament of which this plant is composed, 

 two papillae in close proximity are produced. One of these becomes 

 ultimately developed into a horn-like organ, more or less spirally 

 twisted, in the middle of which, but at no very definite point, a 

 septum is formed, cutting off the apex from the base. The other 

 papilla forms a lateral protuberance, at first symmetrical, but which 

 afterwards throws out a beak-like process (rostrum), "on the side 

 turned towards the horn. A'septum is then formed at the base of 

 this protuberance, cutting it off from the parent tube. After the 

 formation of the septum in the hornlet, minute rod-like bodies are 

 seen imbedded in its colourless mucous contents. In the mean- 

 time an internal layer of colourless substance, called by Pringsheim 

 the cutaneous layer, increases to such an extent, especially in the 

 fore-part of the rostrum, that at last the membrane of the latter is 

 ruptured, and a portion of the cutaneous layer escapes. 



Just at this period the horn opens at it apex, and the contents 

 escape in the form of very minute rod-like corpuscles, which enter 

 the orifice of the sporangium, and penetrate the portion of the 

 cutaneous la^'er which remains. After this a membrane is formed 

 around tlie contents of the sporangium (which were previously bare), 

 and thus a cell is formed, which completely fills the sporangium — 

 the embryonic cell of the plant. This embryonic cell, which is at 

 first green, becomes colourless, with one or more dark-brown bodies 



* See Ann. des Sc. Nat. Vol. vii. p. 43. 



t A summary of these observations was given in the Quarterly Journal of 

 Microscopical Science, Vol. iv. p 63, and 124. 



On the same subject, see Schenk on Vaucheria, Wiirz. N. Z. Vol. ii. p. 201 and 

 Nachtrag zur Kritik, &c. (Pringsheim) in " Jahrbucher f iir wiss. Bot." Vol. ii. 

 p. 470. 



