304 
Psyche 
[December 
into woody capsules. In one case it was observed that both 
it and the mites had attacked the rudimentary leaves of the 
same bud. The close association and limitation of these two 
parasites to the same host and same portion of the host may 
possibly be used to explain the very wide distribution of the 
mites over the same plant and over all the host plants in the 
neighborhood, even when these are widely scattered. The 
mature mites may be disseminated by the winged Pachyp- 
sylla females when the latter seek out the new buds in the 
early spring migration. This migration period of the hemip- 
teron coincides nicely with the requirements of the mites 
for favorable infestation, occurring as it does before the 
buds expand. 
In a mixed group of species of Celtis (C. australis , C. 
Bungeana, C. Douglasii, C. laevigata, C. occidentalis, and 
C. occidentalis canina) in the Arboretum it was possible to 
experiment with the limitation of the mite to its host plant. 
To make sure that it was not because it could not reach the 
other species of the same genus of host plant artificial in- 
festations were carried out. None of the other species of 
the host unaffected under natural conditions reacted to the 
mites placed in their buds, or else the mites failed to find the 
host suitable and did not attack it. These infestations merely 
substantiate the condition of limitation or specialization of 
a species to a single host species, a condition that appears to 
be very general in the Eriophyidse. 
Eriophyes rudis dissimilis subsp. n. 
Host: Betula lutea Michx. f. 
The typical species of this mite was described by Canes- 
trini from Betula verrucosa Ehrh. and Betula pubescens. 
Nalepa (1898) attributed to it the formation of both the 
erineum of the leaves and the bud deformation of these 
hosts. Later, in 1919, he differentiated the form producing 
the bud deformation and associated with a witch’s broom 
formation on B. verrucosa as a subspecies, calycophthirus, 
of the typical rudis found in the erineum. In their list of 
galls and producers Ross and Hedicke (1927) give B. nana, 
