SCIENCE-GOSSIP. 



291 



from dead organic matter ; and parasites which 

 acquire their nutriment from living plants and 

 animals. In his definition of the parasitism of fungi 

 the author defines saprophytic fungi as " those 

 which make no attempt to penetrate the tissues of 

 living plants, but derive their nutriment from a 

 dead substratum." On the other hand, parasitic 

 fungi " are those which, stimulated by the 

 cell contents of another living plant, penetrate 

 wholly or partially into its tissues and draw their 

 nutriment from that source." There are inter- 

 mediate species of fungoid cryptogams which 

 cannot be classed with either parasites or 

 saprophytes. One section of these "attempt to 

 effect an entrance 

 into tissues of living 

 plants by the secre- 

 tion of some fluid or 

 ferment, but only 

 attain their object 

 after first killing the 

 part they attack." 

 The other section 

 are those " forms 

 which inhabit wood 

 of trees, but have not 

 the power to pene- 

 trate through the 

 outer tissues. They 

 depend on first gain- 

 ing entrance through 

 wounds into dead 

 parts of the bark or 

 wood, and, after 

 living there for a 

 time as saprophytes, 

 extend into the living 

 elements, and cause 

 their death." True 

 saprophytes are 

 those which regu- 

 larly pass through 

 their whole life- 

 history in a sapro- 

 phytic manner. 



This class of cryptogams are not treated in 

 Dr. von Tubeuf's book before us, which deals 

 chiefly with the true parasites that undergo 

 no part of their development as saprophytes, 

 but live in every stage of existence as para- 

 sites. There are also included the hemi-parasites 

 and hemi-saprophytes. The former are capable, 

 if need be, of becoming saprophytes for a season, but 

 as a rule they live throughout their whole develop- 

 ment as parasites. The latter usually pass through 

 their lives as saprophytes, but occasionally are 

 capable of existing wholly or partially as parasites. 

 Some of these may be termed ' ' occasional parasites. ' ' 

 for under certain conditions they become parasitic. 



M 



EriciiLoic TvrniN.\ forming white circles on grass stems 

 (From "Diseases of Plants.") 



The " Uredineae, or rust-fungi, may be taken as 

 the most typical of the true parasites. They con- 

 stantly pass through their whole life-history on 

 living plants, and cannot be cultivated on a dead 

 substratum." The same may be said of the 

 Erysipheae, or mildews, though their spores not 

 infrequently reach perfection on a dead substratum, 

 as do also those of Rhytisma and Poly stigma. Ergot 

 of grain and the Sclcyotinia inhabiting berries are 

 truly parasitic, though they may be in some stages 

 saprophytically cultivated on dead organisms. 

 These maybe given as examples of true parasitism. 

 Chapter ii. of Dr. von Tubeuf's work is upon 

 " Reaction of Host to Parasitic Attack," and will 



be found of highest 

 value to the reader 

 interested in mal- 

 for mat ions and 

 abnormal growths 

 among plants. In 

 dealing with this 

 subject the author 

 reminds us that 

 " The reaction of the 

 host to the attacks 

 of parasitic fungi is 

 fairly constant for 

 the same host and 

 fungus. The various 

 fungi, however, exert 

 on the same host- 

 plant each an influ- 

 ence of its own, while 

 different host-plants 

 behave very differ- 

 ently under attacks 

 of the same fungus." 

 Among the more 

 conspicuous of 

 altered growths 

 familiar to most of 

 our readers are the 

 " witches' - brooms," 

 which are composed 

 of many thickened 

 twigs in bunches on various trees. These are the 

 altered growths of the hosts caused by parasitic 

 attacks of the fungoid group Exoasceae, of which 

 the large genus Exoascus is typical. One section 

 of the species of this genus attack the ovary or 

 other part of the fruit, whilst the others attack 

 the shoots or twigs. 



We give, by permission of the publishers of the 

 English edition of " Diseases of Plants," examples 

 of some of the illustrations which are so 

 excellent in this fine work. An effective one is 

 fig. 265, a scene in the Bavarian Forest, near 

 Bischoffsreut showing a living beech-tree with 

 sporophores of Polyponis fomcntarius. Another is 



