974 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 dicecious 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 Hymenodiwm crinitum; but p 
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 
