THAXTER. — MONOGRAPH OF THE LA H< > I IJi I ■; X I A< '] ■;. 1 ■; . 



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Of abnormalities more or less directly due to environment and resulting from growth under con- 

 tinuously unfavorable conditions, as for example exposure to violence or insufficient nutrition, numerous 

 instances might be cited in which the general form and the character of the appendages may have been 

 thus modified. The most remarkable instance, which appears to be of this nature, is seen, however, 

 in the genus Dichomyces, and results in a structural variation which may be in the nature of a reversion. 

 In several species, especially when large numbers grow crowded on the legs of swiftly running hosts, the 

 normal symmetry is lost and the individual assumes a structure exactly like that of the genus PeyrU- 

 schiella, although under favorable conditions, as on the abdomen, this form never appears. Such a 

 condition of D. incequalis was formerly figured and described as a new species of Peyritschiella, P. nigres- 

 cens, and it seems not impossible that this phenomenon may be comparable to reversions resulting from 

 injury in the higher plants. That abnormal forms due to hybridization may exist, has already been 

 suggested above, and this may account for the confused variations seen, for example, in Dichomyces vuU 

 galas or D. princeps. Laboulbenia melanotheca, also, may possibly be nothing more than a hybrid be- 

 tween L. Mexicana and some of the species with black perithecia often associated with it, although this 

 is of course a mere suggestion. 



The Geographical Distribution of the species and genera is now sufficiently well known in many 

 instances to illustrate various points of interest in this connection, but in view of the limitations of the 

 present paper as to space, and the fact that large additional collections of these plants are now awaiting 

 examination and study, no general summary or tabulation of distribution will be here attempted. Infor- 

 mation in regard to distribution is most complete in reference to parasites of the Carabidae; since this 

 family of beetles is a favorite group among entomologists, and is extremely well represented in a majority 

 of the exotic collections examined. Since, also, these insects include a majority of the hosts infested by 

 species of Laboulbenia, it is in this genus that the most complete data as to special instances of distribu- 

 tion have been obtained. A brief reference to the subject will be found below under this genus, but it 

 may be remarked in this connection that it is singular to find a species like L. variabilis infesting a variety 

 of common genera in both American continents, yet quite unknown elsewhere; while the distribution 

 of L. Pheropsophi is coextensive with that of its host in five continents. Of the numerous species on 

 Galerila in South and Central America none extend to Africa, where Galeritw are numerous in species, 

 and are attacked by a single form only, unrelated to the South American one. Again L. Philonthi, which 

 is the common form in North and South America on members of the very large and universally distrib- 

 uted genus Philonthus, is unknowm from other regions, although almost unlimited material has been 

 looked over; while L. cristata, the only species growing on members of the large and varied genus 

 Paderus, has been found from all the continents. 



The Development of Series in the Laboulbeniales, the directions in which this development has 

 proceeded, and the determination of what characters may be considered primitive or the reverse, are mat- 

 ters of interest concerning which, how r ever, the writer finds himself unable to arrive at any satisfactory 

 conclusions. On the assumption that these plants have been derived from aquatic ancestors, one would 

 naturally look to the existing aquatic forms, rather than the terrestrial ones, for suggestions as to primi- 

 tive conditions. The aquatic forms which possess compound antheridia, as is evident from the structure 

 of Limnaiomyces, are identical in type, and closely related to, the much more numerous and more highly 

 developed terrestrial genera of the Peyritschiellacese, and the same njay be said of the often very highly 



