THE EXTENT OF DODDER PARASITISM. 



By E. J. Hill. 



IN the Plant World for January (\"ol. I., page 52), Mr. Willard N. 

 Clute mentions the omnivorous parasitism of one of our common 

 dodders {Ciiscuta Gronovii), the statement being added that it 



would be interesting to know how many kinds of herbs and 

 shrubs it attacks. In 1891 and 1892 I made some special studies upon 

 the dodders with this end in view, carefully identifying all specimens 

 taken in the field, and carried home for study, on which the parasites 

 were found. The identifications could in nearly all cases be made 

 specific. 



The species of dodder in the vicinity of Chicago are C Gronovii^ 

 C. hiflexa, C. temiiflm-a^ C. arvensis^ C. chlorocarpa and C. glomerata. 

 Those with the widest range of host plants were C. Gronovit, arvensis 

 and tenuiflora, though chlorocarpa comes well up in the number. 

 From the groups of plants attacked by the first three at least, the con- 

 clusion was reached that their hosts might be universal in character, 

 and that the more restricted number, in the case of some others, was 

 due rather to the less abundance of the species than to any lack of 

 ability to use certain plants for hosts. The case of C. glomerata 

 was diiTerent. It was limited to species of Heliaiithus and Solidago. 

 Its mode of coiling and its rope-like character, when in fruit, need an 

 upright stem, with leaves few or remote for its proper development, 

 and the straight columnar stems of Helianthns and Solidago, whose 

 lower leaves usually die and fall early, and which branch but little till 

 near the top, are well adapted to this. The dodder also grows in open, 

 sunny places where many of the sunflowers and golden-rods abound. 

 So far as I have seen it confines itself to a single stem, twining 

 directly upward as far as it grows. Other dodders shoot off on branches 

 and bridge open spaces among their hosts and thus make a tangle of 

 stems. These habits, rather than any appetency of nourishtnent in 

 the host of C. glovierata may account for its restriction, a mechanical 

 rather than a physiological necessity, though the two have doubtless 

 cooperated in modifying the species by interaction. 



A list of plants on which C. Gronotni hasheen found is given, some 

 additions from other localities and other years of observation beino- 

 added. A similar list could be made for C. arirnsis and C. tenuijlora. 

 Many hosts were doubtless overlooked, though the areas covered were 

 carefully searched. The nomenclature used is that of Gray's Manual 

 as noted at the time of collection. Specific names of trees and large 

 shrubs pertain to young stages of growth. The list is as follows: 



