INTRODUCTION TO CRYPTOGAMIC BOTANY. 339 



to the structure as to remove closely allied species into different 

 groups, on account of this anomalous appearance. Perhaps 

 the establishment of the Physomycetous group amongst the 

 simpler Fungi might be objected to on account of the perfect 

 analogy of such genera as Acrostalagvius, and the disposition 

 of the fruit in Badhamia ; but it rests on other considerations, 

 and the question, perhaps, is not so much whether Physo- 

 mycetes be a natural group, as whether Acrostalagmus, with 

 its dualism of vesicles and naked spores, belong really to the 

 group, and not to Hyphomycetes. 



365. We have hitherto spoken of those cases only where 

 the peridia are perfectly distinct, but there are genera, as 

 ^thaUum, Spumaria, and Licea, where the mass is more or 

 less confluent. In Licea, indeed, the tips of the peridia are 

 distinct, while in the other genera the whole mass is so confused 

 that the peridia look like mere membranes amongst the spores. 

 We know of no use to which these plants can be applied ; a 

 few only are abundant and large enough to make their use 

 possible. JEthalium septicwm is the pest of hothouses; and 

 other species, especially a Licea, have increased occasionally so 

 much in cucumber and melon frames, as to interfere seriously 

 with their culture. Dr. Wollaston found the spores of Eeticu- 

 laria maxima to yield a phosphoric glass, and, from their 

 great uniformity of size, suggested that they might be em- 

 ployed in minute measurements. It is, however, doubtful 

 whether the identity of size is sufficiently accurate to enable 

 the observer to avoid error. These plants are found in various 

 forms in most parts of the globe ; they descend as low as New 

 Zealand, and occur in high northern latitudes; while the 

 tropics afford many beautiful species, which, however, have not 

 been studied so much as they deserve, because of the difficulty 

 of preserving them for the herbarium. Arcyria punicea and 

 Stemonitis fusca are found in very hot and in very cold 

 climates. yEihalium septicum is produced equally in woods, 

 and in the hot damp air of the stove, a situation in which 

 some other species thrive. One peculiarity is their indifference 

 as to the matrix on which they grow. The same species may 

 occur on plants of the most distant natural affinities, and on 

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