1900] Leavitt, — Relation of plants to atmospheric moisture 31 
Precipitation of dew was thus wholly precluded, and yet the roots 
were exposed to the action of a greater proportion of vapor than 
usually obtains in nature. If at the above humidity the roots were 
found to be unable to win a supply of water, then it would seem that 
their condensing power must be unimportant or wanting. 
As to the evidence from cut roots, this may be said in favor of its 
admittance, viz., that the roots of epiphytes, as Schimper points out, 
play a considerable róle in assimilation. The growing tips are intensely 
green, and the parenchyma under the velamen is provided with chloro- 
phyll. In one West Indian Angraecum, indeed, the roots have 
usurped the function of leaves, so that except at the flowering season 
the plant body consists almost wholly of roots. From the physiological 
standpoint, therefore, cut roots may be considered fairly perfect 
wholes. 
It must be granted, however, that the point is open to objection ; 
and Dr. Goodale has proposed a method of using whole plants which 
seems the most satisfactory mode yet devised. Thus far the results 
obtained by this method accord with those obtained from cut roots. 
The genera represented (by twenty-four species) were Dendro- 
bium, Epidendrum, Peristeria, Scuticaria, Laelia, Cattleya, Burling- 
tonia, Brassavola, Cymbidium, Brassia, Selenipedium, Vanda, Cypri- 
pedium, Oncidium, Angraecum, Masdevallia, Odontoglossum, and 
Maxillaria. From many of the species several different roots were 
used. 
The trials lasted in each case from two to four days, and in a few 
cases much longer. Some roots were taken from unwatered plants, 
and after weighing were put at once into the damp-box. Others were 
left in the laboratory until very dry to the touch, but put to the test 
while the tips were still green and turgid. The cut ends were usually 
waxed or otherwise sealed. 
In all cases a diminution of weight was ascertained. The shrivel- 
ing was often astonishing. Control roots from some of the same 
plants, having access to liquid water, kept vigorous and active in the 
same box. The manner of the drying up was significant. It began at 
the cut end and traveled toward the still turgid terminal portion. The 
latter seemed to be drawing water from the older parts. At any rate 
the velamen was entirely unable to supply, out of the abundant vapor 
at hand, the needs of the suffering cells beneath. 
Since my work with cut roots was completed, the Centralblatt has 
