Higher Cryptogamia and the Phanerogamia. 445 



impregnate this ; while Suminski asserts that the end of a sperma- 

 tozoid becomes developed into the embryo here, just as Schleiden 

 asserts the hollow tube to form the embryo in Phanerogamia. 

 After a time this cell begins to divide, and it is gradually con- 

 verted into an embryo (PL XVII. B. fig. 2) with a bud above 

 and a radicle below, from which grows up the regular leafy stem 

 of the Fern*. 



The prothallium often goes on growing for a long period in a 

 barren condition, even becoming multiplied by throwing off por- 

 tions which grow out as lobes from its margins ; antheridia gene- 

 rally present themselves in these. The archegonia are rarer, and 

 as a general rule only one of these becomes developed into a stem 

 on each prothallium. The fact of impregnation rests solely on 

 the evidence of Suminski and Mercklin, the latter of whom 

 states that it is so difficult to observe, that he only met with 

 spermatozoids in the canal of the archegonium three times in the 

 course of a twelvemonth^ s investigation of the subject. 



In this family we find a more complete exemplification of the 

 " alternation of generations,^^ for the spore produces a thalloid ge- 

 neration (the prothallium) on which the sexual organs are deve- 

 loped, then the archegonium or ovule gives origin to the fully- 

 formed plant composed of stem, leaves, and roots, multiplying 

 by a totally different process, namely the development of spores 

 consisting of simple cells. The sporiferous plant is here of in- 

 definitely long life, as, for example, in the Tree-ferns ; — the pro- 

 thallium on the contrary, unless it remains sterile, is of very short 

 duration f. 



Equisetace^. 



This family has been shown by Thuret, Hofmeister, and others 

 to resemble the Ferns in its mode of reproduction. Its spores 

 produce in like manner a prothallium^ which however is more 

 lobed and ramified, and of much longer duration than that of the 

 Ferns ; upon this are developed antheridia and archegonia, from 

 the latter of which arises the bud, which gives origin to the new 

 perfect spore- bearing Equisetum plant. The Equiseta thus stand 

 very close to the Ferns, the one family exhibiting the proponde- 

 rating development of the leaf, the other of stem in the ulti- 

 mate, spore-bearing form or second generation of the cycle. 



* I have followed out the greater part of the stages of development of 

 the Ferns as described by Hofmeister, and can bear testimony to the ge- 

 neral correctness of his statements. I hope shortly to publish a complete 

 account of the germination from my own observations. 



t It may be mentioned that Hofmeister's researches on the development 

 lead him to regard the Fern fronds as branches and the ramenta as true 

 leaves. 



