GROUP I. THALLOPHYTA: FUNGI: ^CIDIOMYCETES. 



305 



gonidium, termed a uredogonidium, of an orange colour, is formed by abstriction 

 (Fig. 214, III) ; in consequence of the great development of cells at these points 

 the epidermis of the host is ruptured, and the groups of uredogonidia are visible 

 on the surface as rusty spots. These uredogonidia are scattered by the wind, and 

 infect other Grass-plants; on reaching a leaf, the uredogonidium germinates at 

 once, forming a hypha which enters through a stoma into the interior of the 

 leaf, where it developes into a mycelium bearing uredogonidia. This stage in 

 the life-history is termed the Uredo-form. 



Later in the season, when the tissues of the hosts are becoming hard and 

 dry, the Uredo-form no longer produces uredogonidia, but dark-coloured often 

 compound gonidia, known as tcleu- 

 togonidia (Fig. 214, II), developed in 

 the same way as the uredogonidia. 

 The teleutogonidia remain quies- 

 cent during the winter. When 

 they germinate in the following 

 spring, one or both of the cells 

 gives rise to a small, free, non- 

 parasitic mycelium (promycelium), 

 from each of the cells of which a 

 delicate gonidiophore is produced, 

 which developes a small gonidium 

 (termed a sporidium) by abstriction 

 at its apex (Fig. 215). 



The sporidia are scattered by the 

 wind, and if they fall on the leaves 

 of the Barberry they germinate, 

 giving rise to a hypha which 

 pierces the epidermis of the leaf, 

 and then forms a dense mycelium 

 in the intercellular spaces of the 

 mesophyll. At certain points the 

 tissue of the leaf is hypertrophied, 

 forming cushions, which project 

 on the under surface. Towards 

 the upper surface of the cushion 

 there are formed on the mycelium 

 small receptacles, the spermogonia 

 (Fig. 214 sp), each of which con- 

 tains a number of unseptate hyphte, radiating from the wall towards the centre, 

 which are termed sterigmata ; each of these produces at its apex by abstriction 

 a small cell, the spermatium, which escapes from the spermogonium ; spermo- 

 gonia are formed, though less frequently, on the under surface. Large spherical 

 structures are formed ou the under surface of the cushion (Fig. 214) ; these are 

 the aecidia. This form of the fungus is known as dEcidium Berberidis. Each 

 secidiuru consists of a hy menial layer of simple unseptate sporophores at its 

 base, from the apices of which a number of spores (cecidiospores) are formed by 

 successive abstriction ; the secidium has a definite wall which ruptures at the 



a 



A. 



FIG. 215. Germination of teleutogonidia of 

 various Uredineae : A of Puccinia Gra minis ( x 

 400); B of Melampsora (x 300); C of Coleo- 

 sporium ( x 230) ; t teleutogonidium ; pm pro- 

 mycelium ; sp sporidia. 



V. S. B. 



