EFFECT OF PARASITIC FUNGI ON TIIK FoK.M <>F HOST-PLANT. 31 



Somewhat doubtful cases are the outgrowths resembling aerial 

 roots which arise on Laurus canaricnsis attacked by _V/,/^.s/'</////// 

 /"////. Geyler, their discoverer, regarded them as deformed stem- 

 shoots, but they resemble rather the galls of the alpine-rose. 



6. EFFECT OF PARASITIC FI'Nd >X CELL-( 'oNTKNTS. 



The most common and, at the same time, most apparent 

 effect of parasitic fungi in this direction, is the stimulation to 

 cell-division and cell-multiplication. This occurs chiefly in 

 young tissues, or in those still in process of growth, and gives 

 rise to numerous peculiar outgrowths and swellings, some of 

 which have already been referred to. 



The parenchyma of mature tissues may also exhibit secondary 

 cell-division, when under the influence of a parasitic fungus. 

 This I found to be the case in leaf- 

 petioles of Umbellifeiu- attacked by 

 Protomyces macrosporus (Fig. 9). The 

 epidermis and vascular bundles are never 

 disturbed, but the intervening tissues are 

 permeated by an intercellular mycelium, 

 which causes the cells to divide into a 

 lar"-e number of delicate-walled chambers, 



I-'K.. 9. Secondary cell-dlvlaion 



all containing nuclei smaller than those inparenchyj 



is :i result "t I' 



of neighbouring undivided cells. Tin ...... idol of the 



now o-ii> ;nv much smaller tbau 

 same thill" is observed in plants of those of the primary oelL " 



L . pare Fig. 47.) (v. Tubcui .U-l.) 



odorata inhabited by Urocystw 



the mature parenchymatous cells become divided up 

 by means of delicate walls running in various directions into 

 numerous chambers or secondary cells, which Wakker in 

 describing has named "nutritive tissue." 1 This new tis-ue 

 remains permanently in attacks of Protomyces, but with l. r r- 

 ///.s/t's it i> almost completely used up during the lormation 

 of .-pores. In some diseases caused by Kxousceae, a similar 



ndary cell-ilivisjoii takes jdacc ; Ibr example, in the sub- 

 .pidermal parenrhyma of Leaves "f poplar with '/'"/*// ////-' 

 aurea ( I-'ig. (J." i. 



An interestin -r\-ation was made by Elosen s mi the direct 



" Untersuchungen." /'////./-.//.///('<././/(//'.//, !* 

 l:.. .11. Beitrdgi :. l\<nnini^ <i. /'/fan .//://. HaKil. Srhrifi, ivi-j. 



