GENERAL INTRODUCTION 3 



a foothold on dry land, possessed two distinct types of reproductive 

 organs, the primitive type of sexually produced ones, and the 

 modern or conidial form, evolved soon after tlieir adoption of an 

 aerial home. So successful has this modern conidial form of repro- 

 duction proved to be, that in the great majority of instances the 

 older sexual mode of reproduction has been abandoned. In the 

 thousands of gill-bearing fungi or toadstools, also the woody bracket- 

 fungi ; in other words, in the extensive group of fungi technically 

 known as the Basidiomycetes, there is not a vestige of the ancient 

 sexual form of reproduction left, and all tliese fungi are reproduced 

 by the newer conidial method. It may be stated that the Basidio- 

 mycetes is the most modern group of fungi, that is, it is the last 

 to evolve from the series of families that have come into being, or 

 gradually evolved one from another, since the fungi became terres- 

 trial in their habits. For this reason the Basidiomycetes may 

 also be looked upon as representing the most marked type of true 

 fungi, and have shaken off all the indications of their origin from 

 the algae ; in fact, if the Basidiomycetes amongst the fungi alone 

 existed at the present day, it coulcl not have been suggested that 

 they had evolved from the algae ; other groups of fungi, from which 

 the Basidiomycetes originated, how^ever, clearly indicate such origin. 

 Where two or more distinct forms of reproductive bodies are 

 present, which is general in all groups except the Basidiomycetes, 

 as previously defined, each form of reproduction has its own special 

 function sharply defined. The function of the conidial stage, which 

 may be looked upon as a supplementary one, evolved to meet new 

 conditions when the fungi adopted dry land as their habitat, is 

 for the purpose of extending the geographical area of the species, 

 whereas the ancient sexually produced fruit is produced for 

 the purpose of continuing the species in time, or from one 

 season to another. This comes about as follows. Probably the 

 white mildew, so common on the leaves and stems of roses, both 

 wild and cultivated, is familiar to all, or at all events may soon 

 become so, on account of its great frequency, by anyone sufficiently 

 interested in the subject. Now if a mildewed rose leaf is examined 

 with a pocket-lens, the white mildew will appear to resemble a thin 

 coating of wheat flour dusted on the leaf. If a minute portion of 

 this meal, placed in a drop of water, is examined under a microscope 

 magnifying about three hundred times, the apparent powder will 

 be seen to consist of colourless, oblong bodies, or conidia, or summer- 

 spores, as they are often called. These conidia are capable of 

 germination the moment they are mature, and being readily 

 dispersed by wind, insects, birds, etc., some are certain to alight on 

 the leaves of other rose trees, which become infected and quickly 

 produce a crop of conidia which are dispersed in turn, and infect 

 other plants. The production of this conidial form of reproduction 

 continues throughout the growing season, and as myriads of 



