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-tubes 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 Pucdnia graminis 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 Aeddium 

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

 within narrow limits in the host, as Aeddium Leguminosarum ; more often it spreads 

 widely in it, as Aec. Kuphorbiae cyparissiae, Endophyllum 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 Aeddium Leguminosarum and Aec. Tragopogonis ; in 

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

 of Pucdnia graminis (Aec. Berberidis] are formed only on the leaves of Berberis 

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

 dt.) ; in the same way the large aecidia of Roestelia cancellata are found only on the 

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

 species are termed heteroedous (metoedous), to distinguish them from those first named, 

 which are autoedous. 



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

 spores, as in Endophyllum^ 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. Endophyllum Sempervivi is an excep- 

 tion to this rule, inasmuch as its aecidiospores produce promycelia, and Pucdnia Dtanthi, 

 in which the sporidia from the promycelium of the teleutospores send their germ-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 Uromyces, two united 

 together in Pucdnia, three so united in Triphragmium, 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 Roestelia and Pucdnia Dianthi. 



For a more detailed account of the development of these Fungi I choose Aecidium 

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

 its teleutospore-form as Pucdnia graminis. 



