81 



wishes to demonstrate the effect of nourishment on the develop- 

 ment of the reproductive organs in fern prothalHa. 



Fertile fronds of the species to be used should be collected as 

 soon as the spores are ripe. After drying them, by placing them 

 before an open window for a few days, they should be wrapped 

 in paper and placed in a covered pasteboard box in a cool, dry 

 place. When preparing the spores for sowing, shake a frond 

 over white paper or a clean glass plate. Crush the sporangia 

 obtained with a scalpel or a microscopic slide, being very careful 

 not to crush the spores. The spores should be freed from the 

 remains of the sporangia before sowing them and this may be 

 done by rubbing the crushed mass through a sieve of varying 

 thicknesses of silk bolting cloth (which may be procured from a 

 flour mill) stretched in a small embroidery hoop. By adding or 

 removing a thickness of the cloth the grade of the sieve can read- 

 ily be adjusted. 



The most successful of the various methods tried for sowing 

 the spores is as follows : A mass of spores is taken on the point 

 of a scalpel and the instrument is moved over the capsule about 

 half an inch above the surface of the medium, while the spores are 

 gently blown upon. In this manner the spores are fairly evenly 

 distributed. This should be done as quickly as possible and the 

 cover of the capsule replaced in order that the culture medium 

 is not exposed so long to the air. Likewise, whenever examining 

 or removing prothallia from a culture, do not leave it uncovered 

 any longer than is necessary. Never invert a cover. It is well to 

 make up a number of cultures, one or two for each table of the 

 different laboratory sections with a few in reserve. 



After the cultures are made it is best to place them before a 

 window, preferably an east window, where they are exposed to 

 the direct sunlight for a part of the day. This is especially nec- 

 essary during the period of germination. If the cultures are 

 started in warm weather it is best not to allow them to remain in 

 the sunshine longer than one or two hours at a time as the pro- 

 thallia do not develop as well when the culture solution becomes 

 heated. The spores of some species fail to germinate if the cul- 

 ture solution remains too warm. The optimum temperature for 



