290 THE MICROSCOPE. 



drawn off, and the bottle be exposed to the light of the sun, 

 the Desmidiacece will remain unaltered for a long time. 



Fungi. — ^This interesting class of cellular flowerless 

 plants are chiefly microscopic, many requiring a high magni- 

 fying power to determine their peculiarities of structure. 

 They abound in damp places, among decaying and decayed 

 vegetable and animal matters, everywhere, and in almost 

 every place. The structure of all Fungi exhibits a well de- 

 fined separation into two parts, a mycelium (thallus) jointed 

 and branched, forming a kind of cottony filamentous mass, 

 and a reproductive spore or fruit, which, although exceed- 

 ingly minute, differs somewhat in appearance under the 

 microscope. The "spawn" used for planting mushroom 

 beds is composed of mycelium, and may be readily obtained 

 for examination (fig. 188, No. 19). The dust- like powder 

 of any of the moulds or mildew when sprinkled on a slip 

 of glass and kept under a bell glass over water, will soon 

 throw out filaments and spores in all directions. 



De Bary's observations show that resting-spores are not 

 peculiar to the algae ; for he found them in two genera of 

 fungi, and Tulasne ascertained their production in Perono- 

 sporas, many of which are parasitic, as P. parasitica, a 

 species found on the cabbage and turnip leaf, as well as 

 on the shepherd's-purse, Capsella bursapastoris. For the 

 growth of P. infestans, the potato mould, the exclusion 

 of light seems to be needful, and it is easy to conceive 

 how the spores, washed down to the tuber during heavy 

 rains, throw out germinating threads, which easily pene- 

 trate the thick cuticle of the potato, and quickly produce a 

 murrain. 



The Ptev. M. J. Berkeley, our English authority on 

 Fungi, says : — " The genus Cystopus comprises those para- 

 sitic fungi amongst the Uredines which are remarkable for 

 their white spores. Till the resting-spores of the different 

 species were ascertained, it was almost impossible to find 

 good distinctive characters : one species at least, Cystopus 

 candidus, is to be found everywhere on the common 

 shepherd's-purse, and often accompanied by Peronospora 

 parasitica. It is also frequent on the cruciferse : the acro- 

 spores, or gonidia, which spring from the swollen threads 

 of the mycelium, form necklaces, as in oidium, the joint 



