422 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



and Lycopodium, there is a transition from short spiral and 

 reticulated cells to elongated cells, which may be called spiral 

 vessels. Perforated cell-walls are found in a few mosses, and 

 in the stem of Sphagnum tissue occurs just like the so-called 

 glandular tissue of Conifers.* 



463. The most important distinctive character of Acrogens, 

 however, is the complete differentiation of the sexual apparatus, 

 attended by or resulting in peculiarities which separate these 

 plants from all others. If impregnation take place in Thallo- 

 gens, it is by the contact of the spermatozoa or spermatia with 

 the spore or sporidium. At least, such is the case in those 

 Alg83 where the process (p. 89) has been verified.-f- And in 

 those few Fungi (p. 10) where there is an analogue of a pro- 

 thallus, the prothallus has the character of a spore, whether 

 that or the spore of the second order be the body which 

 receives impregnation. In Acrogens, at least those in which 

 spores are produced, impregnation does not take jDlace in the 

 spore itself, but in a distinct organ produced upon the frond or 

 other body to which the germination of the sjoore gives origin. 

 In Characece alone, which approximate Algae, there are spores 

 properly so called ; at least, if the nucule be considered as 

 containing a single solitary spore, but it is not certain whether 

 this is the result or the subject of impregnation. 



464. So much has been said of the habits of Cryptogams in 

 general, and of the relations of the higher forms to Phseno- 

 gams, that it is unnecessary to extend the general remarks, 

 particular information being reserved for each distinct head. 

 It need only be added, that, though the traces of Thallogens 

 in geological strata are for the most part obscure and uncer- 

 tain, we have abundant and undoubted remains of Acrogens, 

 which prove that they performed an important part in the 

 economy of the world before the introduction of man. 



465. I have already, at page 45, given a general notion of 

 the mode of fructification which exists in the higher Crypto- 

 gams. It may be well, however, to restate the matter in a 



* See Hofmeister, Verg. Uutersucli., tab. 13, fig. 8, 8 b. 



t Pi-iugsheim's latest views will be given at the end of this volume. 



