131 



tected in these strands, the tender hyphae are able to spread 

 through areas which are unsuitable for their growth and 

 development, the hyphae being again extruded to absorb 

 nourishment when favourable conditions are met with. 



The fungi may be divided into the following groups : Classifica- 



tion of 



I. Phy corny cetes. Fungi. 



II. Ascomycetes. 



III. Basidiomy cetes. 



IV. UstUaginaceae. 

 V. Uredinaceae. 



117. Phi/corny cetes. The hyphae are 

 generally aseptate. Mycelium does not form a compact m - 7ce 

 mass. Sexual reproduction is common. The asexual spores 

 may be developed in spore-cases ( sporangia), the protoplasmic 

 contents of which divide up to form the spores, or the end cf 

 a hypha may swell up, the swollen tip eventually separating 

 from the hypha to form a spore, which, in such a case, is 

 called a conidium, and the portion of the hypha on which it 

 is borne is called a conidiophore. 



Phytophthora infestans causes the potato disease. This 

 has been selected as a typical example of this 

 group and its life-history is given in detail in Part 

 V below. 



Other species of Phytophthora and species of Pythium are 

 very destructive to seedlings and to palm trees. 



118. Ascomycetes. Hyphse are septate. 



Spores are produced in a special kind of elongated sporangium 

 termed an ascus. The number of spores produced in an ascus 

 is almost always definite, usually eight, whereas in a sporan- 

 gium the number of spores is usually indefinite. In an ascus, 

 also, the protoplasmic contents are not all used up in the for- 

 mation of the spores, as is the case in a sporangium. These 

 asci may be without any covering, or may be grouped in 

 special structures, called the ascocarps, thus forming the ascus- 

 fruits. A completely closed ascocarp is called a cleistothe- 

 cium, one with a small aperture at the apex a perithecium, and 

 one which is open, saucer-shaped, or hat-shaped, an apothecium. 

 Sexual reproduction sometimes occurs. 



Among the interesting fungi included in this group }; 



are the minute, unicellular plants known collectively as the 



Yeast Fungi, or the Saccharomy cetes, which are capable of 



causing the alcoholic fermentation of sugar solutions. \Ve 



Jmow that, if the sweet juice extracted from the sugarcane 



