THE HIGHER CUYPTOGAMIA. 335 



amount of attention from botanists, especially their ger- 

 mination.* The knowledge of them had progressed 

 considerably when Schleiden's well-known work threw the 

 whole subject into confusion. f Schleiden alleged that the 

 small spores (pollen-grains, as he called them) emit a tube, 

 which penetrates into the prothallium developed from the 

 large spores, and is there transformed into the embryo. 

 Schleiden made these statements with a positiveness which 

 would have admitted of no contradiction, had it not been 

 for some almost unaccountable errors of observation. 

 Mettenius, in his beautiful and accurate work, ' Beitrage 

 zur Kenntniss der Rhizocarpese,' did not venture to attack 

 this theory of Schleiden, although he was unable to verify 

 any one of Schleiden's observations. Nageli | never saw 

 the small spores of Pilularia emit tubes, but he made the 

 important discovery that the mother-cellules of the Sperma- 

 tozoa originate in them. lie pointed out anew that the 

 four papillate cells of the mouth of the archegonium — 

 which Schleiden, strange to say, described as " pollen 

 grains seated upon the nucleus, and which had developed 

 tubes " — could not be pollen-grains, but that they rather 

 originated from the prothallium. I published the outlines 

 of the account given above many years ago.§ Mettenius, 

 in a subsequent work, adopted my views. || 



* The earlier literature is fully treated of in Mettenius's work ' Beitrage 

 zur Kenntuess der llhizocarpeen,' Frankfurt a. M., 184-6, p. 1. 

 f ' Grundziige,' 2nd edition, p. 101. 



% 'Zeitschrift f. Botanik./ Heft 3 and 4, (Zurich, 1846.) p. 1S8. 

 § <Bot. Zeit./ 1S49, No. 45. 

 || 'Beitr. zur Botanik./ 1 Heft, Heidelberg, 1850, 



