Arthur: Uredinales of Porto Rico 57 



temperate regions. The generally applanate or pulvinate, strongly 

 colored sori of most rusts of northern regions, render them far 

 more conspicuous than the protected, pale sori, sunken in the 

 tissues or surrounded by paraphyses, more common in the tropics. 

 A growing recognition of this difference led more and more to 

 a search for the inconspicuous, so-called Uredo-iorms on plants 

 of pronounced tropical appearance. In this way each of the 

 two later sets presented a long list of forms that at first could 

 only be classed under the form-genus Uredo. In the Stevens 

 list were 37 such forms, which by careful microscopic study were 

 assorted into 18 forms that could be labelled with published 

 names, 14 that needed to be described as new, and 5 with which 

 other spore forms could be found which permitted them to be 

 placed under true genera. In the Whetzel-Olive list are 31 such 

 forms (exclusive of 3 reduced to synonymy in the Stevens list), 

 which have been assorted into 22 previously known, 4 new, and 

 5 placed under permanent genera. These figures do not include 

 new or old species where the collections showed little or no other 

 form beside uredinia, but which are generally and readily re- 

 ferred to true genera, such as Uromyces appendiculatus, Puccinia 

 Leonotidis, and the species of Coleosporium. 



Although the Whetzel-Olive set contains the same number of 

 species as the Stevens set, allowing for the reduction of some 

 species to synonymy, yet they are not wholly duplicates, as each 

 shows 27 species not found in the other. The Whetzel-Olive 

 material has added 25 species to the recorded rust flora of Porto 

 Rico, 11 of which are new to science, beside permitting the erec- 

 tion of 3 new genera, the arranging of 10 new combinations and 

 bringing to light of many new hosts for previously known species. 

 There are 157 species of Uredinales now reported for Porto Rico, 

 exclusive of Hemileia vastatrix B. & Br., the Asiatic coffee rust, 

 which is dropped from the list because it is believed to be ex- 

 terminated from the island. 



The Whetzel-Olive set provided additional spore-forms which 

 permitted the removal of Uredo concors, U. capituliformis and 

 U. fallaciosa from the form-genus Uredo to their proper generic 

 positions, and in so far assisted in the slow process of classify- 

 ing the host of tropical rusts ordinarily found only in the repeat- 



