326 ALTERNATION OF GENERATIONS IN THE THALLOPHYTES. 



will be necessarily an asexual x^lant, conditions which are accurately 

 fulfilled in those plants {Brifojihijta, .Ptcridophyta) in which an 

 alternation of generations undoubtedly takes place. Since this is 

 so, it appears to be quite unnecessary and even unwarrantable to 

 introduce the idea of an alternation of generations into our general 

 conception of the life-history of Thallophyles. 



There is reason, however, for believing that in two groups of 

 Thallophytes, the Uliaracecp and the ('(>JeocJitrtc<r, a distinct alterna- 

 tion of generations, more or less resembling that of Mosses, occurs." 

 In a previous number of this Journal f I have fully discussed the 

 indications of such an alternation in the life -history of the 

 CharacecB ; it is therefore unnecessary for me to say aiij'thing on 

 the subject in this paper. As regards ColeochcBte, the oospore 

 becomes divided by the formation of successive walls, so that it is 

 converted into a mass of cells united to form a parenchymatous 

 tissue. This mass of cells is the sporophore of the plant, or, 

 according to Pringsheim's view, the " first "neutral generation," 

 which differs but little, excepting in size, from the ordinary thallus.:[ 

 When the wall of the cystocarp ruptures in the spring, the 

 sporophore is set free, and from each of its cells a single swarm- 

 spore escapes which gives rise to an asexual individual. It is only 

 after a long succession of asexual generations, continuing through 

 the whole summer, that sexual plants are produced. Pringsheim, 

 in an earlier publication, § pointed out the homology of the body 

 thus formed in the oospore of ColeocJucte with the sporogonium of a 

 Moss, a view to which he still adheres. The alternation, in this 

 case, is that of a sporophore with a succession of x3otential 

 oophores terminated by an actual oophore ; it deviates from the 

 Moss-type in the intervention of a number of potential oophores 

 between the sporophore and the true oophore ; it is, as it were, a 

 middle term between the fortuitous succession of sexual and 

 asexual generations in Thallophytes generally, and their regular 

 alternation in Mosses and Ferns. 



From this point of view, Pringsheim's expression for the 

 sporophore oi Coleochcete, ''first neutral generation," is inadmissible, 

 for it suggests that the sporophore is of the same nature as the 

 ■ succeeding generations, and this, as we have seen above, is not the 

 case. Moreover, it suggests also that the sporophore of ColeucluHe 

 is of the same nature as the "first neutral generation" of the 

 (Echxjoniedi, of BulbocJucte, Spliaroplea, Hudrodictijon, Paiidorina, 

 and Ctjstopus, where it is simj)ly a sporangium, or of Mucor, where 

 the vegetative organs are developed to some extent. Now 

 Pringsheim has already pointed out, in the last-mentioned 

 publication, that in those Thallophytes which exhibit " sjiorarif/icn- 

 hrimunff,'' the changes taking place in the germinating, or more 

 correctly, the developing zygospore or oospore suggest rather the 



* Possibly this may be also true of the Floridea : see Pringsheim, Ueb. 

 Befruchtunj,' imd Keimiing der Algen ; Monatsber. d. Berl. Akad.. 1855. 

 t December, 1878. 

 J At least in C. scutata. 

 § Die Coleochaiteen : • Jahrb. f. wiss. Bot.,' Jl. 



