Again, the curious distortions on the stems of nettles attacked by the Aecidium form of the heteroecious Puccina (]aricis (see FUNGf for Heteroecism), or on maize stems and leaves attacked by Ustilago Maydis, or on the inflorescence of crucifers infested with Cystopus, &c., are not individually very destructive; it is the cumulative effects of numerous attacks or of extensive epidemics which eventually tell.
This is the only case of heteroecism known in the vegetable kingdom outside the Uredineae.
The eu and opsis forms may exhibit the remarkable phenomenon of heteroecism, i.e.
Heteroecism is very common in this group and is now known in over one hundred and fifty species.
In all cases of heteroecism the sporidia infect one host leading to the production of aecidiospores and spermatia (if present), while the aecidiospores are only able to infect another B /., f.