THE HIGHER CRYPTOGAMIA. 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 Rhizocarpeae,' did not venture to attack 

 this theory of Schleiden, although he was unable to verify 

 any one of Schleiden's observations. Nageli j 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. He 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 Kemitncss der lihizocarpeen/ Frankfurt a. M., 1846, p. 1. 

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



% ' Zeitschri'ft f. Botanik.,' Heft 3 and 1, (Zurich, 1816,) p. 188. 

 f 'Bot. Zeit.,' 1819, No. 15. 

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



