(399) 



It is worthy of note that the species inhabiting § Sabina are 

 divided between the eastern and western continents, while of those 

 inhabiting § Oxycedrus, at least 3 are distributed in both eastern 

 and western hemispheres. In seeking to discover what might 

 account for such a distribution one can scarcely avoid the sug- 

 gestion that the phylogeny and distribution of the hosts may have 

 been an important factor. It seems to be generally accepted that 

 § Oxycedrus, with its subulate leaves, is of earlier origin than 

 § Sabina, with its leaves awl-shaped when young and scale-like 

 when mature. The same species of § Oxycedrus, J. communis 

 and /. sibirica, are widely distributed over the cooler temperate 

 regions of all the continents of the northern hemisphere. Such a 

 wide distribution must have occurred during a geological period 

 when the land conditions permitted migrations between the 

 northern continents. If the species of Gymno sporangium were 

 parasitic on these forms at this early time we would expect them 

 to be widely distributed along with their hosts. Although no 

 fossil species of Gymno sporangium are known, the existence of 

 other fossil fungi makes the assumption of the existence of Gymno- 

 sporangium at this age not improbable. If § Sabina has developed 

 from § Oxydecedrus and has done so since the continents have been 

 isolated, we would not then expect to find the same species, either 

 of hosts or fungi, indigenous in North America and in the Old 

 World; and this, indeed, is the case so far as the writer has been 

 able to learn. 



As to why there should appear to be so many more species oc- 

 curring on § Sabina in North America (18) than in Europe (3) a few 

 suggestions may be offered. In the first place it may be said that 

 the field and culture work of the writer has all been done in North 

 America and that owing to this work the number of species known 

 here has been somewhat extended in recent years, while similar 

 studies have not been carried on to the same extent in Europe. 

 The ratio 18:3 may therefore not represent the actual conditions but 

 is to be taken to represent the conditions as they are now known to 

 the present writer. In the second place, even with the fullest studies, 

 the balance might be expected to be in favor of North America, 

 partly because of the relatively greater development of the species 

 of this section (Sabina) here than in Europe, but chiefly because 

 of the larger number of species and far more complex development 

 of the family Malaceae, the hosts of the alternate phases. 



