370 REPRODUCTION 



under specified conditions; account must be taken, however, of the 

 carbon source and its concentration (257, 305). In general, high con- 

 centrations of nitrogen suppress sporulation (109, 153, 250). 



Specific effects of particular compounds are often reported but can- 

 not be combined in a general theory; pH effects and contamination 

 of organic nitrogen sources with growth factors unduly complicate 

 interpretation of experimental data. Asparagine, so often a favorable 

 source of nitrogen for growth, generally represses sporulation (5, 28, 

 208, 226, 257). The asparagine effect may arise from ammonia accumu- 

 lation or may be another example of the competition between vegeta- 

 tive growth and reproductive activity. It should also be noted that 

 asparagine, of the sources of nitrogen tested, is the best for perithecium 

 formation in Diaporthe phaseolorum (286). 



The effect of hypoxanthine (or guanine) on zygospore formation in 

 Phy corny ces blakesleeanus is probably not specifically a reproductive 

 phenomenon and is considered elsewhere (Chapter 12). The very- 

 striking positive effect of low concentrations of histamine on zygospore 

 formation in P. blakesleeanus (250) merits reinvestigation. 



8. MINERAL NUTRITION 



Numerous observations, some of which have been mentioned in 

 Chapter 9, attest to the influence of mineral nutrition on sporulation; 

 these are reviewed in more detail by Foster (101). As expected, either 

 deficiencies or excesses of particular elements reduce or inhibit sporu- 

 lation; these reactions require no further comment. The important 

 question is whether the mineral requirements for sporulation differ 

 qualitatively or quantitatively from those for growth. 



There is no evidence for a qualitative difference, i.e., sporulation 

 never requires an element which is non-essential to growth. Quanti- 

 tatively, however, there are differences, most of which are subsumed 

 in the generalization that sporulation is reduced by partial deficiencies 

 in certain elements much more than growth is reduced by the same 

 deficiency. Experiments with copper almost invariably show that 

 sporulation of Aspergillus niger is reduced drastically by a deficiency 

 which has a small or even no effect on dry weight (205, 211, 246, 269, 

 270, 313). This copper effect is found also in work with Penicillium 

 spp. and Phoma betae (205). The effect of copper deficiency on spore 

 pigment has been noted earlier (Chapter 9). 



The same phenomenon — sharp reduction in sporulation with only 

 a small decrease in growth — occurs with partial deficiencies of iron 

 (246) or manganese (26, 155, 193, 269, 270). It is a general rule, even 



