28 REACTION OF HOST TO PARASITIC ATTACK. 



may also be seen amongst lower cryptogamic plants, two cases 

 of which may be mentioned here.^ Plcotrachclus ftdgcns, 

 inhabiting the mycelium of Piloholus lUcinii, causes the 

 formation of galls and the suppression of sporangia, while at 

 the same time zygospores, normally rare, occur in large 

 numbers. Likewise a species of Synccplialis parasitic in Piloholus 

 cnjdal linns causes suppression of sporangia and stimulates 

 formation of zygospores. 



The transformation of tioral organs may reseml)le that observed 

 by De Bary, in which, as a result of attack of Pcronospora 

 violacea on Knautia arvensis, the stamens appeared in the form 

 of violet petals. Doubling of flowers is also caused, as in 

 Saponaria officinalis, under the influence of Ustilago saponariae, 

 and Cornpositae with Pcronospora radii. 



The Ustilagineae, perhaps, cause the greatest amount of varia- 

 tion on the flower, because many of them produce their spores 

 in the floral organs of their host. Thus, in the anthers live 

 Ustilago violacea, holostei, scabiosae, intermedia, succisae, hetonicae, 

 'major, scorzonerac, capcnsis, pinguicolac, Vaillantii, and Tuhvrcinia 

 primulicola ; the last named also occurs in ovaries and stigma. 

 So also do many others inhabit the ovary or some other part. 

 Many, like Ustilago mayclis, form spores throughout the plant 

 as well as in the flower, and bring about hypertrophy and 

 destruction of parts. Amongst these are Ustilago avenae, 

 pcrennans, hordei, nuda, tritici, panici miliacei, reiliana, crncnta, 

 sorghi, Crameri, caricis, tragopogonis, Tilletia laevis, etc. 



Cystopus (Fig. 35) causes very characteristic hypertrophy 

 of all parts of the flower, particularly an enormous outgrowth 

 of tlie ovaries and floral envelopes, whereas other parts are 

 arrested in their growth. Wakker investigated a number of 

 Cruciferae with flowers deformed by this parasite, and found 

 variations in the form and anatomy of the deformations 

 produced on the different host-species. 



ExobasidiiLm also causes well-marked hypertrophy of flowers, 

 and even of the whole inflorescence of cowberry. Woronin ^ 

 describes and figures such cases (Fig. 256). All parts of 

 the flower may be attacked and grow to a great size, becoming 



'Zopf., Bdtru(ie zur Physiol, unci Morph. niederer Or<ianUmen, 1892. 

 Zopf., "zur Kenntniss d. Infections-Krankheiten nied. Thiere u. Pflanzen." 

 Nova Acta d. k. Leop. -Carol. D. Akad. Halle., 1888, p. 356. 

 - Naturforsch. Cesellschaft Freiburg-i.-B., 1867. 



