322 XXIII. REPRODUCTION OF FUNGI. 



with a low power, the colourless hyphae will be seen spreading 

 over the surface of the stem, and especially crowded at the 

 position of collapse, while the external tissues of the host will 

 show manifest signs of disorganisation. Teasing out a fragment 

 with needles, the hyphae are seen to be highly refractive, abun- 

 dantly branched, only here and there septate, spreading over the 

 surface, and penetrating it, occasionally by the stomatic clefts, but 

 generally by perforation through the epidermis. Within the host- 

 plant the hyphae can be traced, partly in the intercellular spaces, 

 partly in the cortical cells themselves, the solution of the walls 

 being effected by means of a cellulose-ferment. If a healthy 

 cress seedling be placed in a watch-glass of water for twenty 

 to twenty-four hours, with a fragment of an infected seedling, the 

 attack of the healthy seedling by hyphae from the infected one can 

 be followed, and in a few days gonidia will be developed. Many 

 of these will be seen terminating branches, within or outside the 

 host-plant, in the form of pear-shaped, and later on, spherical 

 swellings ; while many others will be found in intermediate parts 

 of the hyphae ; so that the gonidia can be either terminal or inter- 

 stitial. The gonidia are filled with granular protoplasm ; each is 

 cut off by a septum. They are asexual reproducing bodies. If 

 the tissues are allowed simply to decay, these gonidia are set free, 

 and lie dormant as resting spores. If, however, fresh water 

 is added, or they are transferred to a fresh specimen, they germi- 

 nate in a few hours, one or more germ-tubes being produced. 

 Even in a fresh supply of water, with no Lepidium material, they 

 will germinate, but quickly die. If sown immediately after separa- 

 tion the gonidia produce zoospores, resembling those in Fig. 115. 



If a piece of Lepidium material, with a large number of 

 gonidia, be placed in a pretty considerable quantity of fresh 

 water the sexual organs can often be readily produced, even 

 in a few hours ; or a small w T ell-selected piece may be cultivated 

 in a suspended drop. Examination at frequent intervals is de- 

 sirable, and the development of the oogonia and antheridia, and 

 processes of fertilisation may be followed. With patience in 

 observation the same structures may often be found developed 

 from gonidia in the general culture. 



In general appearance the oogonium resembles the terminal 

 gonidium, is spherical, and cut off from the parent hypha by a 

 septum. When fully formed the contents of the oogonium 

 have separated into a central granular mass, the oosphere, and 



