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KNOWLEDGE & SCIENTIFIC NEWS. 



[Oct., 1904. 



stated that at the present day provisions are made in 

 almost every civilised country for studying fungus 

 diseases, and for imparting practical information on 

 the subject to farmers and horticulturists. In this 

 country the Board of Agriculture is the headquarters 

 in this' matter, aided by various colleges and societies. 

 .Svmbiosis or mutualism are terms expressing a con- 

 dition of things where parasite and host mutually bene- 

 fit by their u'nion. Lichens are the most pronounced 

 examples of this condition of things, and even here the 

 combination retains rriany of the characteristics of a 

 more pronounced type of parasitism, where the plant 

 attacked suffers from every point of view without any 

 compensating factor. For instance, the_ algal and 

 fungal constituents of a lichen each loses its own in- 

 dividuality, and is incapable of performing those 

 functions' which are natural to it as a free and in- 

 dependent entity. 





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The Hawthorn Cluster=cup Fungus. ( 1 1 The first condition parasitic on 

 a Juniper branch inatural size) ; (2I the second condition growing 

 on a living pear leaf (natural size). 



In many other instances where a parasitic fungus 

 attacks a particular host plant, the latter is not killed, 

 but on the other hand the part attacked, which is 

 often sh.arply localised and modified, continues to grow 

 from year to year. This is very clearly seen in the 

 dense tufts of branches popularly known as " witches' 

 brooms " or " birds' nests," so common on many of 

 our forest and fruit trees. 



Such developments, which are frequently of large 

 size and very conspicuous, present marked differences 

 in structure ;ind habit to the normal portion of the 

 tree on which they arc grdwing. I'Or instance, the 

 branches of "witches' brooms" .alwavs grow erect, 

 the leaves are feebly developed and almost destitute of 

 chlorophyll, and are hence incapable of assimilating 

 food ; finallv, such portions nexer bear flowers. Now, 

 from the above statement, it will ha\e been gathered 

 that such combinations of fungus and host plant are 

 incapable of furnishing themselves with food, and in 

 realitv lead in turn a parasitic life on the normal part of 

 Ihc tree of which thev form a portion. 



It mav, perhaps, be well to state that not every 

 " bird's nest " seen in trees is caused by a fungus. 

 For example, the dense tufts so common in many birch 

 trees are caused by a very minute mite. 



Allusion has already been made to the fact that 

 many fungi assume a very different appearance both in 

 form, size, and colour, during different periods of their 

 development. These contrasts are in many instances 

 so pronounced that the various phases of one and the 

 same fungus were at one time considered as entities or 

 distinct species, and allotted positions in the classifica- 

 tion of fungi widely separated from each other. 



Loose smut of oats, V M tla'^o avfUir , (1) Ear of oats infected (natural size); 

 (2) spores of the fungus highly magnified) ; (3) spores germinating 

 and producing minute secondary spores (highly magnified). 



Our knowledge at the present day that certain forms 

 are but links in the chain of one species depends on 

 what are termed pure cultures. This means that one 

 form or condition of a fungus, grown under condi- 

 tions which prevent the possibilit}' of contamination 

 from outside sources, eventually produces the second 

 condition ; while this, in turn, again gives origin to 

 the first condition. 



As an illustration of a fungus appearing under two 

 remarkably different forms, and growing on different 

 plants during certain stages of its life-cycle, may be 

 mentioned the destructive parasite popularly known 

 as hawthorn cluster-cups. The first or spring condi- 

 tion, called Gvmno^porangium clavariafnrme, grows on 

 the common juniper tree, where it causes the infected 

 branches to assume a swollen or gouty appearance. 

 During the month of Mav these swollen portions be- 

 come covered with dull orange-coloured, gelatinous, 

 finger-like bodies about half an inch long. When 

 examined under the microscope, these orange gela- 

 tinous masses are seen to consist entirely of a ma.ss of 



