386 CLASS BASIDIOMYCETEAE 



the witches' brooms so characteristic of some rust infections on Conifers. 

 Dodge (1923) showed that in leaves of Rubus infected by the orange 

 rusts {Kunkelia nitens and Gyntnoconia peckiana (Howe) Trotter) the 

 production of stomata which is usually confined to the lower epidermis is 

 also brought about in the upper epidermis. (Fig. 127.) 



The monocaryon mycelium is of rather short duration in the leaves 

 and stems of herbaceous plants. In woody plants it may persist for years, 

 e.g., Cronartium rihicola Fischer, in the tissues of the white pine {Pinus 

 strohus L.) or Gymnoconia peckiana and Kunkelia nitens in Ruhus where 

 the mycelium penetrates to the roots and infects the new shoots next year. 

 From this mycelium arise the spermogonia (pycnia). These may be sub- 

 cuticular or subepidermal on leaves, green stems or fruits, or even sub- 

 cortical on woody stems. They consist of a basal pseudoparenchymatous 

 mass of uninucleate cells from which arise numerous parallel slender 

 uninucleate sporophores. In these the nucleus divides and the upper 

 daughter nucleus passes out into a terminal sperm cell (pycniospore) con- 

 taining very little cytoplasm and surrounded by a thin cell wall. This 

 spore is pushed loose by the formation of a second sperm cell below it, etc. 

 At the same time a sugary slime is secreted which partially or completelj^ 

 fills the cavity of the spermogonium. The subepidermal spermogonia may 

 be more or less spherical structures with a marginal series of paraphyses 

 around the sporiferous portion. These push up through the epidermis, 

 rupturing it and producing an ostiole through which the sugary slime 

 containing the sperm cells exudes as a shining drop which is sweet in 

 taste. Sometimes the mass of spermogonia is fragrant. The more diffuse 

 subcuticular and subcortical spermogonia also rupture the overlying 

 cuticle or cortex respectively, exposing the sugary exudate. Various in- 

 sects, particularly flies, attracted by the sweet liquid and accompanying 

 fragrance visit the spermogonia and feed on the exudate and go from leaf 

 to leaf and plant to plant. In this way the sperm cells adhering to their 

 feet or mouth parts become scattered widely over various plants or other 

 parts of the same plant. Rain also doubtless helps in the dissemination of 

 the sperms. (Fig. 128.) 



From the same mycelium that has given rise to the spermogonia and 

 often near to these or on the opposite side of the leaf the hyphae begin to 

 mass themselves, frequently at first in a substomatal chamber or other 

 large intercellular space. Eventually this becomes a pseudoparenchy- 

 matous mass of cells, those nearer the surface being larger and less filled 

 with food, the underlying cells being smaller and better supplied with 

 food, the whole mass being more or less surrounded by several layers of 

 hyphae. All the cells are normally uninucleate. This structure is called an 

 aecial primordium. Buller (1938) suggested for this structure the term 

 proto-aecidium. Massee (1888) reported the presence of an oogone with 



