300 



PART IV. CLASSIFICATION. 



Towards the upper surface of the cushion there are formed on the my- 

 celium small receptacles, the spermogonia (Fig. 178 sp\ each of which con- 

 tains a number of uuseptate hyphse, 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 spermo- 

 gonium ; spermogonia are formed, though less frequently, on the under 

 surface : the significance of the spermogonia and spermatia is not known. 

 Large spherical structures are formed on the under surface of the cushion 

 (Fig. 178) ; these are the aicidia. This form of the fungus is known as 

 sEcidium Berberidis. Each secidium consists of a hymenial layer of simple 

 unseptate sporophores at its base, from the apices of which a number of 

 spores (cKcidiospores) are formed by successive abstriction; the secidium 

 has a definite wall which ruptures at the surface to set free the spores. 



JJ. 



FIG. 180. Transverse section of a Willow-leaf FIG. 181. Germinating resting. 



infested by Melampsora salicina -. par mesophyll 

 of leaf: eo upper, eu lower epidermis. On the 

 under side a gorus of uredospores (st) with para- 

 physes (p) has broken through the epidermis ; 

 beneath the upper epidermis is a sorus of young 

 teleutospores (t). (x 260.) 



spores: A of Vstilago receptaculorum ; 

 B of Tilletia Caries ( x 460) : sp the 

 spore ; pm the promycelium ; d the 

 sporidia : in B the sporidia have 

 coalesced in pairs at e. 



The secidiospores are conveyed by the wind to Grass-plants, on the leaves 

 of which they germinate, putting out hyphse which penetrate into the 

 interior through the stomata, giving rise to the mycelium which bears 

 the uredospores, and subsequently the teleutospores. 



Order 2. Ustllagineae. This order comprises those parasites which are 

 known as Smuts. The life-history of most of the members of this order 

 is briefly as follows. The plant produces numerous thick-walled, often 

 black (Smut) resting-spores, the development of which is usually inter- 

 calary (resembling that of chlamydospores) on more or less specialised 

 mycelial branches (conidiophores). On germination, the resting-spore 



