REPRODUCTION OF THE CRTPTOGAMIA. 749 



cases, and hence we may also fairly conclude that it is neces- 

 sary in all, although not absolutely proved. Flowerless plants, 

 however, have no true seeds containing an embryo, but are 

 propagated by spores (page 367), which either reproduce the 

 plant directly, or give rise to an intermediate body, called the 

 pro-embryo or pro-thallus {fig. 784, p), from which the fructiferous 

 or fruit-bearing plant ultimately springs (see page 368). Much 

 difference of opinion has arisen of late years, amongst botanists, 

 as to the mode in which reproduction takes place in the diffe- 

 rent divisions of the vegetable kingdom. The detailed dis- 

 cussion of these different views would be incompatible with the 

 object of an elementary manual of botany, and we shall content 

 ourselves, therefore, with a general summary of the more im- 

 portant conclusions which appear to be most in accordance with 

 our present knowledge upon so difficult a subject. 



1. Keproduction of Cryptoga3ious or Acottledonous 

 Plants. — We have already described the structure of the repro- 

 ductive organs of these plants (sec pp. 367 — 393), and in doing 

 so, M'e treated of them in two divisions, called respectively, Acro- 

 gens and Thallogens, each of which was again sub-divided into 

 several natural orders. We shall follow the same aiTangement 

 in describing their modes of reproduction, except, that we shall 

 here commence with the Thallogens, and proceed upwards to 

 those plants of a more complicated nature, instead of alluding 

 to them, as we then did, in an inverse order. 



A. JReprod action of Thallogens. — The sexuality of plants in all 

 the natural orders of Thallogens has not been absolutely proved, 

 but only concluded by analogy. In the Algie alone, have sexes 

 been clearly shown to exist. The reproductive organs of 

 Fungi and Lichens having been already described, and as no- 

 thing is positively known as to the mode in which they are re- 

 produced, it will only be necessary for us to give a summary of 

 the modes of reproduction in the Algae or Sea-weeds. 



Beprodiiction of AJgce. — The existence of sexes has been 

 proved in members of all the sub-orders of Alga;, although 

 the actual impregnation of the female corpuscle has only been 

 directly observed in four of them, namely, in the Volvocineae, 

 Diatomaceag, Chlorosporeae, and Melanosporere. 



The fecundation of Alga; takes place in two very distinct 

 ways, namely, by conjugation, and by the direct impregnation of 

 naked spores or germ corpuscles by ciliated spermatozoids. Each 

 mode is also subject to modifications. We can only briefly al- 

 lude to the subject here. 



1. Conjugation. — This process has been noticed in the Diato- 

 macese generally, and in certain Chlorosporeae. It consists in 

 the union of the contents (endochrome) of the cells of two fila- 

 ments (fronds), (fig. 828), and the formation of a germinating 

 spore by their mutual action. No difference can be detected in 



