128 FIRST GROUP.— THALLOPHYTES. 



the epidermis of the acicular leaves of the pine in spring, and the teleutospores 

 develope promycelia as they lie, and these form sporidia, the germ-lubes of which 

 penetrate into the young leaves and spread through them, and this mycelium gives rise 

 in the next year to new teleutospores. We must suppose that these genera 

 have lost the aecidia out of the course of their development and have retained only 

 the gonidia. The Basidiomycetes, to be described further on, afford a still more 

 remarkable instance of a Fungus reproducing itself only by gonidia. It must be 

 mentioned here that such species as Puccinia granmiis supply a transition from the 

 Uredineae which have aecidia to those which have not, in so far as the aecidia are of 

 rare occurrence with them, while gonidia are formed in abundance. 



The spermatia are produced in peculiar receptacles, the spermogonia (Fig. 85, 

 sp) containing small branches of the hyphae, from which the spermatia are abscised. 

 It has been already intimated that they are very probably to be regarded as male 

 organs of fertilisation. 



The Uredineae are found exclusively in living Phanerogams, usually in the stem 

 and leaves or sometimes in the living cortical tissue of trees, as the Conifers ; the 

 spreading of the mycelium in the intercellular passages of the host does not necessarily 

 disturb the growth of the plant ; but it sometimes disfigures it, as when Aecidiiim 

 elatitium causes the ' witches' brooms ' in fir-trees ; sometimes the mycelium is confined 

 within narrow limits in the host, as Aecidiion Leginninosariiin\ more often it spreads 

 widely in it, as Aec. Et/p/iorbtm cyfiarissiae, Endophylluin Sempervivi. The fructifi- 

 cations as well as the gonidial forms (uredospores and teleutospores) are formed 

 beneath the epidermis of the host, and break through it when they are ripe and so 

 come to the surface. 



Some of the well-known species which have gonidia use the same host for all the 

 stages of their development, as Aecidhan Legwninosarum and Aec. Tragopogonis ; in 

 others the different reproductive forms develope only on dififerent hosts ; thus the aecidia 

 of Puccinia graniinis (Aec. Berberidis) are formed only on the leaves of Befbo'is 

 vulgaris, while the uredospores and teleutospores occur only on grasses (De Bary, loc. 

 cit.) ; in the same way the large aecidia of Rocstelia cancellata are found only on the 

 leaves of the Pomaceae, and their teleutospores only on species of Juniper. Such 

 species are termed heteroecious {jiictoecious), to distinguisli them from those first named, 

 which are autoecious. 



The sporidia produced by the promycelium, whether it proceeds from the aecidio- 

 spores, as in Etidophylluin, or from the teleutospores, send their germ-tubes through 

 the walls of the epidermis into the interior of the host ; but the germ-tubes from the 

 aecidiospores and the uredospores travel over the epidermis till they find a stoma and make 

 their way through it to the intercellular spaces. E>idophyUii)ii Sempervivi '\s an excep- 

 tion to this rule, inasmuch as its aecidiospores produce promycelia, and Puccinia Dia/ithi, 

 in which the sporidia from the promycelium of the teleutospores send their genn-tubes 

 into the tissue of the host through the stomata, is also an exception. 



The germ-tubes of both uredospores and teleutospores issue from them at spots 

 previously prepared, where the cuticularised outer coat (the exosporium) is absent or 

 very thin ; three to six such perforations are found in the equator of each uredospore, one 

 in each cell of a teleutospore. The teleutospores are single in Uroniyces, two united 

 together in Puccinia, three so united in Triphragtnium, four in Phragmidium ; they 

 usually rest for some time before germinating in the spring, but they sometimes ger- 

 minate immediately after their formation, as in Rocstelia and Puccinia Dianihi. 



For a more detailed account of the development of these P'ungi I choose Aecidium 

 Berberidis, whose uredo-form causes 'Rust ' in wheat, and which is also known from 

 its teleutospore-form as Puccinia graminis. 



