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W. B. Grove. 
to the exact requirements. This is P. cohcesa Long. Its sperrnogones 
and secidia agree in every detail with those on Anemone coronaria, 
e.g., among other resemblances, in both the sperrnogones are 
similar in shape and distribution, and the margin of the aecidial 
cups breaks up into a few (usually four) spreading lobes—a very 
unusual circumstance from which AE. quadrifidum derived its name. 
Its uredo- and teleutospores (Fig. I, D) agree equally with those 
on Primus , the sori are the same in size and arrangement, both 
kinds of spores have the same unusual shape and the same surface 
markings, and the uredospores are accompanied by numerous 
capitate paraphyses. Finally, there is one particular detail of 
agreement which must convince the most cautious—the teleutospores 
of both occur in bunches of 10—20 together, all attached by short 
fragile pedicels to a common base. Arthur includes both species 
(P- cohcesa and P. Pruni-spinosce), on this and other grounds, in his 
genus Tranzschelia (I). It is probable, though no investigation has 
been made, that in these cases the teleutospore-mother-cells bud 
off in succession from a common basal cell, as takes place in a smaller 
degree in Leptinia and Chaconia (15) and, as shown by Hoffmann 
(14), in Endophyllum, and by Dittschlag, in Puccinia Falcarice (10). 
Such a wonderful series of congruences suggests at once a 
reasonable explanation. P. cohcesa represents the original species. 
From this P.fusca arose by a shortening of the life-history (by 
dropping out some of the spore forms), a process which is now well 
known to indicate an adaptation to an environment in which the 
saving of time is of importance, as in Alpine districts or on early 
spring vegetation, such as in the case of Anemone. In Switzerland 
the percentage of Micropucciniae is twice as great in the Alpine as 
in the lowland regions; the same is true of the flora of Sweden 
when compared with that of Germany (12). Secondly, P. Pruni- 
spinosce arose by a sudden transference of the uredo- and teleutospore 
phases to another host, as outlined above. In this we can trace 
an agreement with Dietel’s “ Law.” He arrived at the conclusion 
(9), by studying the sequence of the Uredineae, that they have 
evolved pari passu with the plants upon which they are parasitic 
and, as a corollary, that when a mutation took place, leading to a 
change of host, it was almost always in the direction of selecting 
the new one from a group of later (or at any rate, not of earlier) 
evolution than the original host. In consonance with this is the 
fact that the Rosacese, to which Primus belongs, are of a more 
specialised type than the Ranunculaceae, to which Anemone belongs. 
