PHYLOGENY 79 



found that, in Uredinopsis, the teleutospores are irregularly 

 scattered throughout the spongy mesophyll of the host. But, 

 in this position, their germination, or at least the liberation of 

 their basidiospores, could not take place easily until the leaf 

 had decayed. The transference to a place either (1) beneath the 

 cuticle, (2) in the epidermal cells, or (3) just beneath the 

 epidermis, and their aggregation into definite sori which by 

 their upward pressure would burst through the overlying layers, 

 would both be an advance in adaptation; so these various 

 positions are found to be occupied in successive genera, and the 

 most effective of all (the subepidermal sorus) is alone to be met 

 with in the highest groups. 



In regard to a peridium, this can be supposed non-existent 

 at first, (1) because there is no peridium in the Ustilaginales, 

 (2) because a peridium could not exist so long as the trichogyne 

 was functional. 



Here, it is true, there is a little deviation from what might 

 be expected ; a peridium is found in U? , edinopsis, Milesina, 

 Melampsorella and Melampsoridium (round the uredo-sori), but 

 in Hyalopsora this is very rudimentary or completely absent, 

 and it can scarcely be compared, in any case, with the peridium 

 of the secidial stage of Puccinia, being of a very different 

 character. It must be considered as a special development, 

 separately originated for the protection of the uredo-sori in 

 these lower groups. When one considers the secidiospores, one 

 finds them in the intermediate types either without a peridium, 

 or with encircling paraphyses, or with an irregularly shaped 

 peridium, and it is only in the higher forms, such as Puccinia 

 and Uromyces, that the beautifully outlined "Cluster-cup" arises. 



In respect to these higher groups it has been shown else- 

 where (Grove, 1913) that the Endophyllacese constitute the 

 starting-point from which the varied forms of the Pucciniacese 

 have been evolved. A certain amount of advance went on, of 

 course, simultaneously among the Impedicellata?, though to 

 nothing like the same extent. 



In Endophyllum the secidiospore which is the product of the 

 fusion-cell is also the teleutospore which germinates with a 

 basidium : in accordance with theory it is accompanied by 



