184 PLANT WOKLD. 



further attention is necessary excepting to maintain an ade- 

 quate supply of water in the bottle. Under a bell jar very 

 little water is lost, so that the apparatus can stand without 

 attention for months. The cultures behave apparently as 

 they do in nature. It is unnecessary ever to wet the plants 

 by pouring water over them, and danger of mechanical 

 disturbance is thus completely removed. 



This method will recommend itself to workers who 

 desire to study the effect of light, of various gases, and of dis- 

 solved salts on algal growth. It must be remembered, how- 

 ever, that the nutrient medium on the surface of the cup will 

 gradually l)ecome more concentrated if the evaporation rate 

 is relatively high, but it is easy to control evaporation so as 

 to prevent this entirely or reduce it to a minimum. A certain 

 amount of evaporation will, no doubt, be accomodated by 

 backward diffusion of the solutes into the cup and eventually 

 into the bottle. 



The apparatus should be suitable for the growing of 

 mosses from spores as well as for the germination of fern 

 spores and the like. Even small seeds, such as those of 

 certain grasses, and mucilaginous ones, such as those of 

 mustard and other Cruciferse, can be germinated on the moist 

 clay cup. Thus it is possible to obtain material for the study 

 of root hairs, clean and free from soil. The apparatus is so 

 simple and operates so automatically that it is adapted to the 

 needs of teachers who desire good class demonstrations in a 

 form involving a minimum of attention. 



Algae, mosses and fern gametophytes may be grown 

 upon soil which is kept at a constant moisture content by the 

 same apparatus, as described in the Plant World for Feb., 

 1908. A rather heavy soil, loam or clay, has been found 

 most suitable for the growth of algae and mosses by this ar- 

 rangement. They thrive without attention for months at a 

 time. — Burton E. L'rc'Diirslon. 



Munich, July 15, 1908. 



