2 INTRODUCTION [CH. 



inner layer of the spore wall. In such cases one or more germ-tubes may 

 break through the wall of the spore at spots not previously recognizable, or 

 they may find an exit through special pits or germ-pores formed during 

 the development of the spore. The germ-tube elongates and receives the 

 contents of the spore. 



In cases where a mycelium is not developed the plant body consists 

 entirely of reproductive structures (Yeast, Archimycetes). 



The typical fungal protoplast consists of a mass of granular or reticulate 

 cytoplasm, which in the older regions leaves a vacuole in the centre of the 

 cell or filament; the nucleus, where its size has permitted of detailed in- 

 vestigation, has a structure quite similar to that of other plants and animals, 

 and usually divides by mitosis, showing a well-marked spindle with cen- 

 trosomes and asters. The development of the spindle is extranuclear in 

 certain Uredinales. One or more nucleoli are commonly present and are 

 thrown out into the cytoplasm during karyokinesis. The extrusion of chro- 

 matin bodies has been described in Helvetia crispa. 



The cell wall consists of cellulose; often a special variety known as 

 fungus cellulose is present. The storage materials include amylo-dextrin 

 or soluble starch, amyloid, a reserve-cellulose, both of which turn blue with 

 iodine; oil, glycogen, and various protein substances. The protoplasm gives 

 rise also to a number of ferments which not only enable the plant to deal 

 with its food materials, but bring into solution the walls of the host cells, 

 and so make possible the penetration of parasitic hyphae. 



Sexual reproduction among the fungi takes place by the union of two 

 uninucleate or multinucleate cells which may be similar in structure and 

 behaviour, or may be differentiated as an antheridium and an oogonium. 

 Each of these organs contains one or more distinct gametes, or else a number 

 of gametes which do not become rounded off from one another or separated 

 from the wall of the parent cell, but are indicated by separate nuclei lying 

 in an undifferentiated mass of cytoplasm. To organs of the latter type the 

 term coenogamete is sometimes applied in recognition of their multinucleate 

 character; it is, however, inappropriate, since they are not gametes, but 

 gametangia. In the vast majority of fungi free swimming gametes are not 

 developed ; the sole exceptions are found in the genus Monoblepharis, where 

 uniciliate or biciliate spermatozoids are set free and swim to the female 

 organ. 



A state of affairs in which the antheridium as a whole must grow or be 

 carried to the oogonium involves a risk that normal fusion will fail to occur, 

 while at the same time the presence of multinucleate sexual organs and of 

 vegetative cells between which anastomoses readily occur offers considerable 

 opportunities for some form of "reduced" fertilization. The replacement of 

 normal fertilization by the fusion of two female or two vegetative nuclei, or 



