TYPES OF CRYPTOGAMS; THALLOPHYTES 2638 
THE STUDY OF MICROSPHARA 
314. Occurrence. — Species of Microsphera and allied forms 
occur in late summer and fall on leaves of various herbaceous and 
woody plants. The growth is confined to the surfaces of the leaf 
(upper, lower, or both). Among the most available species are 
those which grow upon lilac, oak, grape, cherry, willow, and wild 
plants of the sunflower family. Some species are known to occur 
on only one host-plant, others occur on several or a large number, 
and the host-plants may belong to one or more than one family. 
Besides Microsphera there are about five other genera, any of 
which may be substituted or studied comparatively. They are dis- 
tinguished by the form of the appendages, together with the number 
of spore-sacs (asci) in each sac-receptacle or perithecium. 
The species of fungi which Microsphera represents are called 
powdery mildews. 
With naked eye and magnifying glass examine the surface of a 
leaf bearing powdery mildew. Note which surface and what portion 
of the surface is occupied by the fungus, whether the occupied area 
is restricted or not, the color, and any other characters. 
315. Examination with the Microscope. — Place a small drop of 
water on the leaf where the fungus occurs, if possible where dark- 
colored specks occur among the mycelium. Pick from the leaf a 
portion of the fungus loosened by the water and place with a drop 
of water ona slide. Place a cover-glass over it. Examine under 
a power of about fifty diameters. The dark-colored specks will be 
seen as somewhat spherical bodies ( perithecia). Note their structure 
and color and their appendages. Have the perithecia any regular 
way of opening? Note the length of the appendages as compared 
with the diameter of the perithecia; also note the form of the tips 
and of the base, the color and any variation of color in different 
parts of the appendages. Keep the left hand on the focusing screw, 
and with the needle in the right hand press with gentle but varying 
stress upon the cover-glass to rupture the perithecia. Even with 
great care broken cover-glasses may result, but this pressure should 
force out the contents of the perithecia. Another method is to 
remove the slide from the microscope and, with a pencil rubber 
