518 ALTERATION OF FORM BY PARASITIC FUNGI. 



the autumn in meadows which have been mown in the spring. The flowers appear- 

 ing under these circumstances are remarkable for their small size. Their diameter 

 is at least a third smaller than that of the spring flowers. In conclusion we may 

 refer to the gardener's artifice which has already been described (p. 453) of pro- 

 ducing perennial plants with woody stems from an annual Mignonette plant by 

 mutilation. We might also mention the dwarf shrubs and trees produced by 

 combined mutilation and grafting, especially the strange-looking little Ivy treea 

 obtained by grafting a flowering branch of Ivy on an erect stem a span high, and 

 the dwarf Conifers so much in favour with the Japanese. 



Gardeners and descriptive Botanists have frequently determined and described 

 mutilated plants as other species, hybrids, or varieties. They are neither the one 

 nor the other. The peculiar appearance of the altered members resulting from 

 mutilation is exactly determined beforehand in each species; it is due to the specific 

 constitution of the species, and thus is part of its being. It is not produced by the 

 external influences ■ which lead to the formation of varieties, but is brought about 

 by inherent necessity quite independent of the influences of climate and soil. 



ALTERATION OF FORM BY PARASITIC FUNGI. 



A considerable number of the trees and shrubs of Central and Southern Europe 

 bear bristling, much-branched structures on some of their boughs which, from a 

 distance, look like large birds' nests or brooms, and which have been popularly 

 termed "witches' brooms". They are the outward and visible signs of a disease 

 from which the plants in question suflTer, and, as their name testifies, their origin 

 was thought to be connected with witches. Traditionally witches have the power 

 of "wishing'' harm to mankind, animals, and plants; and superstitious people, at 

 the sight of these peculiar pathological structures on the trees, may have started 

 the idea that the disease was caused by witches that they might have brooms 

 ready at hand for their midnight ride on the Brocken. Other plant diseases have 

 been ascribed to unusual conditions of weather, especially to long-continued rain 

 or great drought. It is not long since the discovery was made that most of the 

 diseases attacking trees, shrubs, and herbs are caused by Fungi, and that atmos- 

 pheric conditions are only concerned in the matter in so far as they hinder or 

 favour the establishment and development of these parasites. 



All the Fungi in question are parasites. They penetrate into the tissues of the 

 host-plant and sooner or later cause the death of the aflfected part, and frequently 

 of the entire host-plant. The living protoplasm in the cells and tissues of the host 

 which is influenced by the parasite undergoes fundamental changes in its com- 

 position. Some of the cells are drained, their living protoplasm being consumed, 

 so to speak, and these cells are obviously marked for destruction. Others are not 

 killed, but changed. The metamorphosis occurs, in the first place, in the consti- 

 tution of the living protoplasts which have not yet completed their development, 

 the change much resembling that known as fermentation in fluid substances 



