INTRODUCTION TO CRYPTOGAMIG BOTANY. 60 



knowledge of the objects themselves, or confusion respecting 

 the proper limits which separate the animal and the vegetable 

 world. They were, a few years since, almost universal in 

 Germany, and were received with favour by a few French 

 Botanists, but have never gained much ground amongst our- 

 selves, except in popular belief In France and England at the 

 present time they are all but exploded, and I am happy to 

 see that German botanists are beginning to follow in the same 

 direction. Some, however, still lean to the old notion, as, for 

 example, Dr. Cohn, in a late article on the mould which is so 

 fatal to flies in autumn, and which he supposes to arise by a 

 free development of vegetable cells in the diseased blood.* With 

 respect to parasitic Fungi, which have been regarded either as 

 mere metamorphoses of the parent cells, or as spontaneously 

 generated, it must be borne in mind that one species at least, 

 Tilletia Caries (the common Wheat Bunt), may be propagated 

 by the spores at will. The infected plants are at once dis- 

 tinguishable from those which have had no contact with the 

 parasite; and, though not the slightest trace of fungal threads 

 can be found in them, it is quite certain that something capable 

 of reproducing the species is present, either in the inter- 

 cellular passages or protoplasm. This is applicable to hosts 

 of fungi of very different affinities which protrude through 

 the tissues of decaying branches. In the case of Botrytis 

 infestans, the fimgus which is, in my opinion, the proximate 

 cause of the potato murrain, the walls of the cavities of the 

 carpels of Tomatoes are often covered with the fungus, though 

 there is no communication with the outward air ; and a crop 

 of the mould has been seen to grow in a few hours from the 

 cut surface of a diseased potato, even though the foliage itself 

 had exhibited no traces of the parasite. 



52. Were spontaneous generation true, and plants produced 

 * Hedwigia, 1865, p. 59. His words are, "The influence of tlie spores 

 of Empusa in the appearance of this fungus, and of the disease in flies, 

 is by no means evident, since the genesis, the chemical and optical cha- 

 racters of the numberless free cells in the blood, the absence of a special 

 expanded mycelium, and above all the whole history of the develop- 

 ment, seem to concur in favour of the origination of the cells of the 

 Em/pxisa from the diseased blood." 

 •5 



