THE FUNGI WHICH. CAUSE PLANT DISEASE 61 



chains, catenulate, Fig. 36, owing to the development of one spore 

 below another before the elder spore is shed. Conidia may be 

 either simple, composed of one cell, or compound, composed of two 

 or more cells. In compound spores each cell is at least potentially 

 a spore and can germinate under favorable conditions and per- 

 petuate the species. In many compound spores the germinating 

 function is sacrificed by one or more of their component cells. 



Conidiophores may consist of loosely branching, rather long 

 hyphae, or they may be short, innate, and in close clusters forming 

 distinct spore bearing 



spots. Fig. 371. Such d^^^ 



sporiferous spots when 

 naked are called acer- 

 vuli. Often the conid- 

 iophores are roofed over 

 with a net-work of 

 woven fungous threads 

 thus constituting a 

 special spore-bearing 

 structure, the pycnidium. 

 Figs. 37, 335. Conidio- 

 phores may be solitary 

 or grow together in bun- 

 dles or branch loosely as 

 in Fig. 383. 



The basidium, Fig. 38, 

 is a special kind of sporo- 



Ohore bearing at its Fig. 37.— Conidia borne in a pycnidium. After 

 ^ „ r Quaintance and Shear. 



apex usually four, or 



two, small projections, sterigmata, each of which produces one 



spore, for distinction called a basidiospore. 



Some fungi bear the spores loose inside of the swollen tips of 

 sporophores as in Fig. 68. The spore bearing structure is then 

 called a sporangium and its stalk a sporangiophore. The ascus 

 is another spore bearing structure. In it the spores are borne very 

 much as they are in the sporangium but usually of definite num- 

 ber, 1, 2, 4, 8, 16, etc., eight being thei most common number. 

 Asci may be naked or covered, scattered or collected in groups. 



