386 Cannon: Anatomy of Phoradendron villosum Nutt. 



appears in the wood cylinder of the aerial haustoria. However, 

 in the latter case the canals appear to be permanent. This point 



needs further investigation. 



The phloem consists of bast parenchyma, of sieve tubes, and 

 companion cells. The sieve plates were difficult to demonstrate. 

 The primary hard bast bundles, typical of the stem, are, of course, 

 not found in the haustoria. 



In comparing the mass of cortex with the mass of conductive 

 tissue in the cortical haustoria with the same in the aerial 

 haustoria we see a decided difference — the cortex preponderates in 

 the former, the conductive tissue in the latter case. This is corre- 

 lated with the change which these haustoria have undergone in 

 function. An index of this change is found in the contents of 

 the cortex of the two sorts of haustoria. Starch grains are found 

 in the cortex of the cortical, but they are not present to any ap- 

 preciable extent in that of the aerial haustoria. That is, the 

 cortex of the aerial haustoria has ceased to function as a food 

 reservoir. The great development of conductive tissue is 

 also indicative of the change from an absorbing organ to ft con- 

 ductive one. 



In concluding this account of the haustoria of the mistletoe it 

 should be said that each of these kinds of haustoria are present 

 in the older plants as well as in the young, and in this regard the 

 American mistletoe does not agree with the European species 

 ( Viscam album). In Visaim there is a sort of tap root from 

 which the lateral roots, cortical haustoria, spring. Frank * does 

 not mention the formation of aerial haustoria in Viscum and he in- 

 timates that such, indeed, are not present, because he says that 

 the connections between the sinkers and the stem, the aerial haus- 

 toria, are sooner or later broken. Although I have not made a 

 close study of the oldest plants, I believe from the manner of the 

 formation and development of the aerial haustoria that in the 

 American mistletoe that connection during the life of the plant is 

 never broken. This must necessarily be the case since the aerial 

 haustoria become an integral portion of the stem. 



* Frank, Die Pfilzplanzen, Krankheiten der Pflanzen, 1896, p. 530 



