THE FUNGI 



91 



arrangement; but in all the higher ones they are borne in 

 definite spore-fruits of characteristic form. This spore- 

 fruit is undoubtedly, in many instances, the result of 

 fertilization, being pro- 

 duced by the formation of 

 a peculiar cell, the archi- 

 carp, which corresponds to 

 the oogonium of the Phy- 

 comycetes. This is usually 

 fertilized by direct contact 

 with the antheridium, and 

 from it, more or less di- 

 rectly, are produced the 

 spore-sacs or asci. 



A good example of these 

 simpler Ascomycetes is 

 offered by the mildews 

 which infest many plants, 

 e.g. Sphserotheca, the com- 

 mon rose mildew. These 

 are true parasites, but grow 

 entirely upon the surface of 

 the host, into whose epider- 

 mal cells are sent suckers 

 by means of which the 

 parasite obtains nutriment 

 from the host. The myce- 

 lium of the fungus sends 

 up vertical branches from 



which are successively cut off oval cells spores or 

 " conidia," - which germinate promptly and through 

 whose means the fungus may spread rapidly. 



FIG. 24 (Ascomycetes) . A, a chain 

 of conidia or non-sexual spores of 

 a mildew (Sphserotheca) , one of 

 the simpler sac-fungi, or Ascomy- 

 cetes, growing upon the leaves of 

 the dandelion ; B, the sexual repro- 

 ductive organs, archicarp, ar, and 

 antheridium, an ; as the result of 

 the fusion of these there is formed 

 the spore-fruit, C, containing the 

 single spore-sac, or ascus, sp, which 

 is derived directly from the fertil- 

 izer archicarp; D, the ripe spore- 

 fruit seen from without; E, a 

 single spore-sac containing eight 

 spores; F, a cup-fungus (Ascobo- 

 lus) ; G, section of the spore-fruit 

 of Ascobolus showing the numer- 

 ous spore-sacs, which are also 

 derived from a fertilized archicarp ; 

 H, a single ascus of Ascobolus. 



