28 REACTION OF HOST TO PARASITIC ATTACK. 



may also be seen amongst lower cryptogamic plants, two cases 

 of which may be mentioned here.^ Pleotrachelus fulffens, 

 inhabiting the mycelium of Pildbolus Kleinii, 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 Syncephalis parasitic in Piloboltis 

 crystalliwus causes suppression of sporangia and stimulates 

 formation of zygospores. 



The transformation of floral organs may resemble that observed 

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

 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 Compositae with Feronospora 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, scaJbiosae, intermedia, succisae, hetonicae, 

 major, scorzonerae, capensis, pinguicolac, Vaillantii, and Tubwrdnia 

 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 maydis, form spores throughout the plant 

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

 destruction of parts. Amongst these are Ustilago avenae, 

 perennans, hordei, nicda, tntici, panici miliacei, reiliana, omenta, 

 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 the 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. 



Exohasidium 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, becominor 



'Zopf., Beitrage zur Physiol, und Morph. niederer Organismeii, 1892. 

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

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

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



