Although much progress has been made in determining the value and constancy of morphological characters, we are still in need of a sufficiently comprehensive and easily applied scheme of classification, partly owing to the existence in the literature of imperfectly described forms, the life-history of which is not yet known, or the microscopic characters of which have not been examined with sufficient accuracy and thoroughness.
The Basidiales are further characterized by the complete loss of normal sexuality, but at some time or other in the life-history there takes place an association of two nuclei in a cell; the two nuclei are derived from separate cells or possibly in some cases are sister nuclei of the same cell.
This group like the rest of the Basidiales exhibits an association of nuclei at some point in its life-history, but unlike the case of the Basidiomycetes the point of association in the Uredineae is very well defined in all those forms which st .:_ possess aecidiospores.
The greater part of his life-history is preserved in late Biblical narratives, which carry back existing conditions and beliefs to the time of the Exodus, and find a precedent for contemporary hierarchical institutions in the events of that period.
While from the nature of their life-history there is no doubt that they have a rather close relationship to the Meloidae, their structure is so remarkable that it seems advisable to regard them as at least a distinct tribe of Coleoptera.
But detailed study of these various groups of insects shows that beneath their common superficial resemblances lie important distinctions in structure, and essential differences in the course of the life-history.
Not only has the number of known forms been greatly multiplied, but the study of the biology and life-history of the parasites has been attended in some cases with remarkable and unexpected results.
Brumpt (5a), Leger (32, 33), Keysselitz (16), Prowazek (47), Minchin (41b) and others - has undoubtedly shown that much of Schaudinn's scheme of the life-history of a Trypanosome is well-founded.
Such a scheme may be placed here in a tabular form before entering on the consideration of the life-history, natural history, morphology, and classification of the several groups: Pteridophyta.
The perithecia are only produced exceptionally in Europe, but this stage of the life-history is common in the United States and causes a widely spread disease among the American vines.