146 Minnesota Plant Diseases. 



are the fungus constituents. The number of lichens in Min- 

 nesota is very great, but a mere passing notice of these 

 can be given here. The constituent fungi of lichens are in 

 reality parasites in the broader sense on the algae, but 

 the latter also derive benefit from the partnership. Obvi- 

 ously, therefore, this group of fungi does not produce any 

 diseases of higher plants. The lichens attach themselves to 

 tree-trunks or limbs where they are held in an advantageous 

 position or they grow on the soil or as crust on rocks. In the 

 latter case they act as the pioneers of vegetative life in the 

 invasion of rock surfaces and are usually the first to obtain a 

 foothold. Lichens have invented a peculiar partnership prop- 

 agative body, which is merely a packet of algal cells, wrapped 

 up in a net-work of fungus threads. When such packets come 

 into proper conditions, they commence growth and build up a 

 new lichen plant. In addition, the fungus produces its proper 

 sac-spores and in many cases accessory spores, but when these 

 germinate the resulting mycelium must soon come into contact 

 with the proper algae or the fungus perishes. This is therefore 

 an uncertain means of reproduction of the lichen and the packet 

 device can easily be seen to have advantages over it in the pro- 

 vision for the algal constituent as well as for the fungus. (Fig. 



21.) 



Morels, saddle fungi and their allies (Helvellinecs). The 

 saddle fungi are very common plants of our woods. They are 

 all fairly large forms and are fleshly. Their relationship with 

 the cup fungi is easily understood by comparison with the long 

 stalked cups whose sac surface is flattened or turned back. 

 Such are in reality the simplest of the saddle fungi. The stalk 

 in some forms, however, becomes channeled and is often hol- 

 low. The cups in many, moreover, are not only turned back as 

 one might imagine a rubber cup to be turned inside out, but 

 the sac surface often becomes convoluted and lobed or ridged 

 so that the sacs may thus be produced over a greater surface. 

 The saddle fungi are usually whitish in color, or may vary from 

 grey to greyish brown. 



In the morels the cup, or as it is here termed, a cap, has 

 very greatly increased its spore surface by the formation of 

 ridges which join and form a network enclosing deep depres- 



