Jantary, 1904. 



KNOWLEDGE 



combined with a complete loss of all trace of sexual 

 reproiliK'tion. 



The iiiiinv causes combined to effect this remarkable 

 chauge cannot be discussed here ; suffice it to say that the 

 transition from an aijuatic to a terrestrial habitat is a 

 main factor. 



The fuuiri are primarily divided into two groups, 

 dej^iending on the mode of oriirin of the spores or 

 reproductive bodies. lu the first or older group, dating 

 from their secession from the alg;e. the spores are produced 

 Inside sjiecial cells called axci, and the s[>ores are leclinically 

 described as axcosjiores. In the older representatives of 

 this group, that is those nearest to the alga-, there is a 

 distinct motle of sexual rej>rodiictiou, in many instances 

 indistinguishable from that presented by many alga;, but 

 as the members invaded dry land tlie .sexual mode of 

 reproiluction gradually disap|>eared, and is now com- 

 paratively rare ; nevertheless the same general form of 

 spore-producing structure is maintained. 



Now as these f uugi became more ;iiid more accustomed 

 to existence on dry land, a most important addition to 

 their meaus of reproduction gradually evolved. This 

 consisted in the development of secondary kinds of 

 rejiroductive bodies, technically called conidia. Now conidia 

 more or less resemble ordinary spores in structure and 

 appearance, but differ in not being a sexual product. 



This group of fungi, collectively known as the Ascomy- 

 cetes, inchides many thousands of different kinds, large 

 muiibers of which are very minute, and known only to 

 those specially interested in the study of the fungi. 



Among kinds belonging to this group, and fairly well 

 known, may l>e enumerated the Morels. Truffles, Yeasts, 

 and certain of the minute fonus popularly known as 

 moulds and mildews. 



The second large group, called the Basidiomycetes, have 

 the spores borne on the surface of special cells called 

 hamdia, hence the spores are spoken of as basidiospores. 

 In this group there is no vestige left of the sexual mode 

 of reproduction. The representatives of this section are 

 usually much larger in size than those of the Ascomycetes, 

 and include such well-known forms as the common mush- 

 room, toadstools, puffballs, and the woody, bracket-shaped 

 or hoof-shaped fungi growing on trees. It has already 

 lieen stated that secondary forms of fruit are produced by 

 fungi, but it is necessary to enter more into detail 

 respecting this matter, as the extremes to which this idea 

 is carried out in certain groups has no parallel elsewhere 

 in the vegetable kingdom. 



In some fungi the different stages which together form 

 the complete cycle of development are as different iu 

 general appearance and relative size as that between a 

 lK>ppv and an ash tree. Not only is this the case but the 

 various forms usually grow at different periods of the 

 year, one may be an annual and the other a perennial 

 condition ; and, finally, when parasites, the forms may 

 grow on different kinds of host-plants. 



As an instance of such multiplicity of forms repre- 

 senting phases in the life-cycle of an individual, may be 

 mentioned the common and very destructive wheat rust. 

 The spring stage of this fungus appears under the form of 

 clusters of miniature cups with frmged edges, filled with 

 orange spores, on living leaves of the barberrv'. The spores 

 of this form are scattered by wind, and those that happen 

 to alight on a blade of wheat soon germinate and enter 

 the tissues, and in course of time produce minute streaks 

 of a rust colour on the surface of the living leaf. The 

 spores of this second condition, dispersed by wind, inocu- 

 late other wheat plants, and as the spores are produced in 

 rapid succession throughout the summer, it can be readily 

 understood how quickly an epidemic of disease can spread 



after a parasitic fungus has once secured an entrance. 

 Towards the autumn, a third form of fruit is produced on 

 the fading wheat leaves, (piite dilTereut in appearance from 

 either of the two stages previously tnentioned. The spores 

 of this third stage are called renting apores, Ijecause they 

 remain unchanged until the following spring, when they 

 germinate and iuDculate young barberry leaves, which 

 results iu the pro<Iucti(in of the first stage of the fvmgus 

 again, and the cycle of develo[imeut proceeds as before. 



Some fungi have two distinct forms iu the life-cycle ; 

 some three, as wheat rust ; some four or even more. In 

 some instances, one form of the cycle can be omitted at 

 times, as in the case of wheat rust, where the stage on 

 barberry is dropped altogether in some countries. 



Thousands of different fungi have tlie individual made 

 up as it were of a number of distinct, different looking 



Fig. 4. — An example of the Ascomjcetes fPeziza acetahulumj. 

 The asei line tlie inside of the cup. Natural size. On the left is an 

 ascus containing eight spores. Magnified 500 tiimes. Not uncommon 

 on the ground in our woods. 



parts growing at different periods of the year under 

 different conditions, and fulfilling varied functions in the 

 life of the complete plant. Tlie use of the quickly-growing 

 summer condition is to furnish an enormous number of 

 spores, by which the fungus is enabled to extend its 

 geographical distribution ; whereas the autumn form, pro- 

 ducing resting spores, is for the purpose of preserving 

 the species in time, by bridging over the period when the 

 plant on which the fungus is parasitic is not growing. 



The various methods of spore dispersion as occurring 

 in the fungi are interesting ; only a few of the most 

 pronounced can be noticed here. By far the most 

 imiversal agent in effecting the distribution of spores is 

 wind, as may be observed when a ripe puffball is crushed 

 under foot. Insects are also answerable for the extension 

 of many fungus epidemics, Ijy alternately feeding on, or 

 visiting diseased and healthy plants, and in so doing 

 unconsciously conveying spores from one plant to another. 

 Perhaps the most interesting instance occurs in a group of 

 fungi to which our " stinkhom " l)elong8. Most of the 

 species are tropical, in this country we have only three 

 representatives. In this group the reproductive portion 



