50 SCIENCE PROGRESS 



of the various external fadtors ; it is thus very difficult to 

 alter one factor without altering others at the same time. In 

 the case of algae and fungi, which can be grown in the laboratory 

 under artificial conditions that can be easily varied at will, 

 the difficulties are not so great, and it is not surprising that 

 in this field of work our knowledge is mostly based on 

 experiments with the lower organisms. The art of growing 

 micro-organisms, such as bacteria, fungi and also algae, in 

 pure culture has been carried to a high pitch of perfection, but 

 since the growth of bacteria and fungi takes place within such 

 wide limits and under a wide range of conditions, the analytic 

 study of environmental factors has been largely neglected in 

 the development of pure-culture methods. Some bacterial 

 parasites of animals are markedly sensitive to temperature 

 conditions, but the majority of fungi will grow within a wide 

 range of temperature so the effect of temperature on the growth 

 of fungi has not been fully studied. Again it is convenient in 

 culture-work to grow fungi in tubes plugged with cotton-wool, 

 i.e. under conditions in which gaseous exchange must be 

 reduced to a low level. Yet, since most fungi tolerate readily 

 such conditions, the effect of aeration on the growth of fungi 

 has been neglected. A certain amount of analytic work with 

 the help of synthetic media was carried out by earlier workers, 

 such as Pasteur and Raulin, and later by Winogradsky and 

 Beijerinck. In 1896 Klebs published the first of his series of 

 papers on the effect of external conditions on algae and fungi 

 grown in pure culture. Klebs did not confine himself to the 

 effect of such conditions on growth, but he studied the effect 

 of external conditions on reproduction also. Klebs put forward 

 the view that growth and reproduction are processes which 

 depend upon different conditions, and that as long as the con- 

 ditions favourable for growth are present, reproduction in 

 the lower organisms does not occur. Klebs brought out 

 also a point of great importance, that the conditions suitable for 

 reproduction are more restricted than those for growth, so that 

 reproduction is liable to be inhibited by too high or too low 

 intensity of some factor. 



It is well known to mycologists and plant pathologists 

 that though there is little difficulty in growing most fungi in 

 pure culture, the production of reproductive organs by fungi 

 under these conditions is quite another matter. Anything 



