ALTERNATION OF GENERATIONS. 145 



in which the impregnated archegonium of a moss should 

 mature but a single spore, germinating directly into its own 

 protonema and moss, as the egg of the viviparous Trema- 

 tode is at once developed without the intervention of any 

 nurse animal into the likeness of its parent. Or again, we 

 might conceive the " fern-spore," while still attached to the 

 frond, developing a prothallium, which might be compared 

 to the flower of the Ruscus aculeatus ; such a prothallium 

 would then stand in somewhat the same relation to the 

 original axis, as the spermatic and ovarian sacs do to the 

 body of the common Hydra. 



Though the discovery of cases like these would no doubt 

 confirm the parallel just indicated, yet, even as the case 

 stands, there seem to be sufficient grounds for assuming 

 the existence among Vegetables, as well as in the Animal 

 Kingdom, of varieties of the so-called alternation of genera- 

 tions, distinguished from each other by the period at which 

 the budding process is interpolated in the cycle of successive 

 forms. 



