1912] REYNOLDS—PARASITIZED LEAF TISSUE 367 
TREUB (79) described the effect of Heterodera upon the root 
structure, and other writers have also studied abnormal root 
structures. 
Stems and branches are oe subject to invasion by parasites 
of various kinds. A somewhat detailed description of the deforma- 
tion caused by Ustilago in the stem of Zea Mays was given by Miss 
KNOWLES (35), while WAKKER (84) showed that many groups of 
fungi have the power of changing the appearance and structure 
of stems. The Exoasceae eause numerous: hypertrophies and 
other abnormalities in the vegetative organs as shown by SMITH 
(70). HartMAn (27) described the witch broom of the white fir. 
Several of our common flowering plants, such as Hepatica and 
certain species of Euphorbia, were described by MEEHAN (43) as 
having elongated petioles and stems when attacked by rusts. 
EBERHARDT (19, 20) gave some histologic data regarding various 
stem tissues in pathologic condition. Some abnormal anatomic 
conditions were described by MOLLiarD (50). 
The effects of disease upon the forms of leaves are among the 
most noticeable of the pathologic phenomena. WoRONIN (932) 
found various modifications of the leaf tissue caused by Exobasidium 
Vaccinii. Exoascus also causes very striking abnormalities in the 
leaves of various species of Prunus that have been described by 
Miss KNowLEs (34), ATKINSON (4), and SmiTH (70). WAKKER (84) 
described various leaf modifications due to fungi. Some histologic 
changes of the needles of the witch broom of the white fir were 
noted by Hartman (27). The observations of Prciion (63) 
showed that other kinds of rusts cause changes in the structure of 
leaves and stems. The anatomic changes caused by species of 
Gymnosporangium were described by W6RNLE (94a); and ANDER- 
SON (1) described the same for Aecidium elatinum on Abies balsamea. 
Plants growing normally in one range of temperature, when placed 
in a colder climate are often noticeably affected. BONNIER (6, 7), 
WAGNER (83), and Hovarp (28) have given us valuable results in 
their studies on this subject. Intumescences caused by abnormal 
environment have been described by Miss DALE (13) 14, 15); 
VON SCHRENK (67a), and others. The effects of various chemical 
substances upon plants have been studied. Of the work on. this 
