i8 DISEASES OF CROP-PLANTS 



below in relation to the manner in which they are produced. 

 The Roman numerals are commonly used for reference. The 

 older terminology is given in brackets. 



L JEcia. (secidia), which typically are cup-shaped structures 

 sunk in the substance of a leaf. The aeciospores (secidiospores) 

 are usually globular, or angular by compression, developed in 

 chains. They are capable of immediate germination and the 

 infection of a suitable host. 



O. Pycnia (pycnidia), very small flask-shaped structures 

 usually, when present, associated with aecia, sometimes with 

 other forms, but never alone. The pycniospores are minute 

 unicellular bodies the function of which is either lost or has 

 escaped detection. 



II. Uredinia (uredo-sori), circular or elongated pustules 

 from which arise stalked roundish unicellular urediniospores 

 (uredospores), often rough or spiny. These are usually produced 

 quickly and in abundance, and, as they germinate at once under 

 suitable conditions, serve for the rapid spread of the fungus. 

 Thick-walled resting forms of urediniospores which occur in some 

 species are distinguished as amphispores. 



III. Telia (teleuto-sori). Mingled in the same sorus with 

 the urediniospores, succeeding them, or in separate sori, may 

 occur teliospores (teleutospores) which typically are stalked, one 

 to several-celled, thick-walled resting spores, but may diverge 

 widely from this form, even to the point of resembling secio- 

 spores. The real criterion of their nature is the manner of germina- 

 tion, in which each ceU produces a germ tube the tip of which 

 divides into a linear row of cells, typically four, each of these 

 giving rise to a short stalk on which one rounded thin-walled 

 spore is borne. This structure is regarded as a basidium, bearing 

 basidiospores, and the Uredinales are accordingly classed as 

 Basidiomycetes. The spores so produced germinate on suitable 

 hosts and produce a mycelium which develops spores of one of 

 the types described. 



One species may possess in its full life-cycle all the forms 

 enumerated; or any or all of them, except the telial stage, may be 

 omitted. It is not, however, necessary that the stages be passed 

 through in sequence ; an indefinite number of generations, for 

 example, may arise from the successive production of uredinio- 

 spores. In the heteroecious species the aecia and pycnia are 

 found on one host, and the uredinia and telia, or telia alone, on 

 another. 



The mycelium of the rust fungi is freely branched and septate, 

 usually intercellular, with haustoria penetrating the cells. 



The commoner rusts on cultivated plants in these islands are 

 the following : Puccinia purpurea, Cke. sorghum rust, very 

 common and generally distributed on guinea corn, imphee, and 

 Sudan grass ; Puccinia Sorghi, Schw. {Maydis, Bereng.), brown 

 rust of Indian corn, rather conmion in some places, but not as a 



