XIIL] "DAMPING OFF" OF SEEDLING-TREES. 287 



of seedlings is due to the triumphant development of 

 fungi belonging to the same genus as the one we have 

 been considering, or else to the closely allied genus 

 Pythium. In illustration of this I will mention one 

 case only. 



It is always possible to obtain well-grown specimens 

 of the fungus Pythium by sowing cress seed fairly thick 

 and keeping the soil well watered and sheltered. Now 

 what does this mean ? Nobody imagines that the 

 fungus arises spontaneously, or is produced in any 

 miraculous manner ; and in fact we need not speculate 

 on the matter, for the fact is that by keeping the crowded 

 cress seedlings moist and warm we favour the develop- 

 ment of the Pythium (spores of which are always there) 

 in somewhat greater proportion than we do the 

 development of the cress. In other words, when the 

 cress is growing normally and happily under proper 

 conditions, it is not because the Pythium is absent, 

 but because (under the particular conditions which 

 favour the normal development of healthy cress) it 

 grows and develops spores relatively so slowly that the 

 young cress seedlings have time to grow up out of its 

 reach. The recognition of this struggle for existence on 

 the part of seedlings is of the utmost importance to 

 all who are concerned with the raising of plants. 



