Lj L I B R •* R Y ■ 3Q 



COMPARATIVE MORPHOLOGY OF 



FUNGI 



CHAPTER I 

 INTRODUCTION 



There are two distinct phases in the cytological development of 

 sexually reproducing organisms, the haploid phase with the single or x 

 number of chromosomes, and the diploid phase with the double or 2x 

 number. The former ends with fertilization, the latter with meiosis. 



A morphological change in the organism occurs parallel and in the 

 same rhythm with this change in nuclear condition and is apparently 

 correlated with it. Certain specialized cells or groups of cells which 

 usually produce the characteristic organs of fertilization, always appear 

 at the transition from haploid to diploid phase, while meiosis occurs at 

 the transition from diploid to haploid phase. According to their cor- 

 responding nuclear phase, these cells or groups of cells are called haplont 

 (haploid soma) and diplont (diploid soma). In an ideal case this cyto- 

 logical and morphological change of phase may be represented by the 

 following diagram: 



r~ pc r i 



Haplont— >Gametangia— >Gametes— >Zygote— > Diplont— >Gonotocont— >Tetracytes— >Haplont 

 Haploid phase Diploid phase Haploid phase 



Diagram I. 



Gametangia containing gametes are formed on the haplont. Plas- 

 mogamy (a fusion between two sexual cells) which is followed sooner 

 or later by caryogamy (a fusion of two sexual nuclei) takes place between 

 pairs of gametes. These two processes are indicated as P and C in the 

 above diagram. The product of fertilization is called a zygote as long 

 as it remains unicellular; it develops into a diplont which forms gono- 

 toconts (organs in which meiosis occurs). The products of meiosis, in so 

 far as they are spores, are called tetracytes and develop into new hap- 

 lonts. In the ideal case, haploid and diploid phases show a similar 

 structure: haplont corresponds to diplont, gametangium to gonotocont, 

 gamete to tetracyte. Fertilization and meiosis are the cardinal points 

 in the life cycle, indicated in the diagram by vertical lines with the 



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