40 THE PLANT WORLD. 



After the apparatus is in position, the seeds or plants are 

 placed in the usual way, and will continue to grow normally 

 as long as the reservoir is not emptied. The soil draws water 

 from the cup and this is kept filled from the reservoir. If 

 water is removed from the soil, by evaporation or by plant 

 absorption, more is simultaneously withdrawn from the cup, 

 so that the moisture condition of the soil mass is kept practi- 

 cally constant. The moisture condition at which the soil is 

 in capillary equilibrium with the cup is determined by the re- 

 sistance offered to the removal of water from the latter, and 

 this depends upon the distance which the supply must be 

 lifted from the reservoir. If it is desired to maintain the soil 

 in a state of saturation the reservoir is placed somewhat above 

 the level of the cup. By lowering the reservoir a drier soil 

 may be maintained, but if the reservoir is too low the soil will 

 be too dry for plant growth. With different soils the level 

 of the reservoir will vary for the same moisture content; for 

 ordinary potting soils and ordinary plants it is well to have 

 the reservoir thirty or forty centimeters below the cup. The 

 level needed is easily determined for any soil by direct ex- 

 periment. The reservoir should be of rather large hori- 

 zontal section in order to prevent the great fluctuations 

 between fillings. Where no attention is to be given the cul- 

 tures for weeks at a time a constant level device may be at- 

 tached to the latter and this connected with the water supply 

 pipe so that filling is unnecessary. The same reservoir will 

 serve for any number of pots. — Burton Edward Livingston. 

 Gibraltar, Jan. 20, 1908. 



A PERENNIAL DODDER. 



Whether a plant maintains its functions in a state during 

 the winter season from which it may succeed to renewed 

 activity upon the advent of spring depends in many cases 

 upon individual peculiarities. Some run their course in a few 

 months, and rarely exhibit the power of persistence, even 



