AUGUST, 1910.] THE ORCHID REVIEW. 229 
I find, on averaging a number of measurements, that pots of Cypripedes, 
potted on ordinary lines, contain a surprisingly large amount of air. For 
example, an empty 5in. pot contains 35 fl. oz. of air; sucha pot filled in the 
ordinary manner with drainage, compost and plant contains, in addition, 
Ir to 12 fl. oz. of air. The volume of air in the drainage is approximately 
equal to the actual volume of drainage material used, .¢., about half the 
space occupied by the drainage in the pot is filled by air, not counting air 
in the pores of the drainage material. In a 5in. pot drained tin. deep the 
air spaces in the drainage amount to about 5 fl.oz. Thus air is a more 
important constituent, by bulk at least, of pot contents than might be 
supposed. As these measurements were made by displacing the contained 
air by water, it is certain that when partly dry the potting materials must 
contain an even larger amount ofair. _I believe that this air is necessary 
in order to imitate natural conditions, but, under ordinary potting con- 
ditions, the air in the drainage can, if the plant is not watered very 
frequently, only contain about the same percentage of water as the air of 
the house. Asa rule ifthe Hygrometer shows 2°-3° of difference, with occa- 
sional variations to, say, 5°, the atmosphere is damp enough for the leaves, 
but I believe that the longer and older roots require a saturated or nearly 
saturated atmosphere, and that, under natural conditions, the rock-growing 
Cypripedes send many roots down into clefts, &c., until they find this 
saturated atmosphere. 
I have often, when repotting plants in fair condition, observed injurious 
or poor growth in roots after they had entered the drainage, and it seems 
not improbable that these injuries are due to too dry an atmosphere in the 
drainage checking the growth of the roots which had entered it. Cypri- 
pedium roots can extend to a considerable length; I have had bellatulum 
roots 2ft. long. I think it probable that under natural conditions the base 
of the plant and the shorter and younger roots are generally surrounded by 
materials which dry readily, and are not constantly wet, while the longer 
and older roots are further down in crevices in saturated or nearly saturated 
air. Under ordinary potting and Orchid house treatment I think that 
these conditions are generally reversed, the base of the plant and younger 
roots being in a moister medium than the older roots which have reached 
the drainage. Having these considerations in mind, I tried placing some 
pots, containing plants, in saucers, and allowing the base of the pot and part 
of the drainage to soak therein for, say, 20 to 30 minutes after watering, 
when the unabsorbed water was poured away and the pot replaced in the 
saucer. The pot being thus closed at the bottom, the thoroughly moist 
drainage produces the saturated atmosphere required by those roots that 
have reached the drainage. 
To produce dryer conditions in the compost, especially near the surface, I 
