Caeoma Apocynaceae. 193 



CAEOMA Link. 



There are several imperfect forms which only occur in one stage and 

 cannot with certainty be assigned to their proper genera. For such it is 

 convenient to have a form-genus, which simply serves as a resting-place until 

 their true affinities are determined. At first they were considered to be 

 independent fungi and had generic names assigned to them. These form- 

 genera are Caeoma, Aecidium, and Uredo, and of the former there are wnlv 

 two known for Australia, one of which was called an Aecidium by Cooke 

 and the other a Uredo by Berkeley. This is not surprising when one 

 considers that the caeoma is not distinct from the aecidium, as in those 

 cases where the one merges into the other. Thus in Puccinia prenanthis 

 (Pers.) Lindr., the aecidial wall is very imperfectly formed, so that the 

 aecidia approach caeoma-forms. Barclay 3 also found a variety of this 

 species in Simla, in which there was not a vestige of a peridium, and 

 he considers this, along with others, an interesting example of an inter- 

 mediate and mostly vanishing stage between Aecidium and Caeoma. In 

 the aecidial stage of Puccinia aucta (Aecidium lobeliae Thuem., A. micro- 

 stomum Berk.), the peridial wall was sometimes absent, so that I described 

 it at first as a Caeoma. 



Caeomata are generally considered to be stages in the life-history of the 

 Melampsoraceae, but since true caeoma-forms occur in connexion with 

 Puccinia, and species such as Melampsora tremulae Tul. have so-called 

 caeoma-forms as Caeoma laricis (Westd.) Hart, with an investment of 

 barren cells, the evidence for this connexion is weakened and the necessity 

 for retaining this as a form-genus much reduced. In Saccardo's Sylloge 

 Fungorum the isolated forms are treated as a sub-genus of Uredo with sub- 

 ^atenulate spores. They have no special significance here, but elsewhere 

 they form witches'-brooms. 



General Characters. They are simply aecidia without peridia, the spores 

 are produced in chains, with or without paraphyses, and accompanied by 

 spermogonia. 



Caeoma-forms, 2. 



APOCYNACEAE. 



Tabernaemon tana. 



129. Caeoma apocyni McAlp. 



I. Sori on both surfaces of leaf, minute, crowded, brownish, bullate. 



Spores yellowish, very variable in shape, ellipsoid, ovoid, pear- 

 shaped, oblong or angular, with finely granular contents, 25-34 

 x 20-26 p. ; epispore hyaline, coarsely verrucose, 5 p. thick. 



On Tabernaemontana orientalis B. Br. 

 Queensland Brisbane, (Bailey 1 ). 



Mr. Bailey kindly sent me a specimen of this from his herbarium, 

 which had been named by Dr. Cooke Aecidium apocyni Schwein., as 

 given in his Handbook of Australian Fungi, p. 341 (1902). It has no 

 pseudoperidium, however, and is therefore a Caeoma, and since the spores do 

 not apparently agree even with those of Caeoma (Aecidium) apocynatum 

 Schwein., it is constituted a new species. 



