374 ON REPRODUCTION. 



Although the spores of many species germinate in pro- 

 fusion, it often happens that no plant bud is formed, even 

 under the most favourable circumstances of atmospheric 

 heat and moisture. This failure of plant bud may be 

 possibly due to the spores being, as above stated, uni- 

 sexual, and therefore producing only dioecious prothallia. 



The time required before the spores germinate varies 

 greatly, some taking eighteen months, others two or three 

 weeks. Some species of Gymnogramma and Cheilanthes 

 germinate in as many days, while Brainea insignis will 

 germinate in as short a time as forty-eight hours. Few 

 prothallia of the latter, however, produce plants, while, on 

 the other hand, Ceratopteris thalictroides germinates 

 quickly and produces abundance of plants, even becoming 

 weeds. 



Of late years some intermediate forms of species, espe- 

 cially of the genus Gymnogramma, have been raised in 

 gardens, which are by some called sports or hybrids, 

 whether such is simply the effect of cultivation, or by the 

 prothallia of two distinct species being so contiguous to 

 one another that the spermatzoids of the one have the 

 power of passing and fertilizing the archegonia of the 

 other, thus generating hybrids, as in flowering plants. In 

 general prothallia produce only a single bud, but on the 

 bud being removed it is succeeded by others, and thus as 

 many as eight or ten young plants have been produced 

 from a single prothallium of Hymenodiiim crinitum; but 

 what is even still more singular, is, that by dividing the 

 prothallia from the base upwards into two or even four 

 parts, each part produces a plant bud. An explanation 

 of this, as also of many other points connected with the 

 subject, is yet to be discovered ; for instance, in 1830, 

 plants of Lomaria Patersoni, a native of Tasmania, made 



