220 Proceedings of the Royal IrisJi Academy. 



they often appear nmch the same. HoTvever, if the haustoria have 

 been long developed, the branch into which the hanstoria have pene- 

 trated presents the appearance of being exhausted, i. e. the cells of its 

 parenchyma are devoid of starch, and their protoplasm is very scanty. 

 In a case where four branches twined together, A sent haustoria into 

 B, and B into C, and lastly D into C. From this it would appear 

 that the branches are not differentiated into those which will act as 

 hosts and those which will act as parasites. For in this case B took 

 on both parts. 



The haustoria developed in these examples of self-parasitism 

 resemble those normally developed ; except that, as a rule, the surface 

 of the haustorium advancing in the tissue of the host branch is smoother 

 than that developed in a true host. In the latter case the superficial 

 cells of the haustorium are usually elongate and lobose : in the former 

 they appear polygonal, not much longer in one direction than in 

 another. Another point of difference between the normal haustoria 

 and those fonned in the parasite's own tissues is that in the latter 

 case tracheides are seldom developed in the haustorium. This, how- 

 ever, is not a constant difference, and a few specimens were found in 

 which a central stand of tracheides was well developed in a hausto- 

 rium connecting two branches of the parasite. Of course the small 

 amount of tracheidal elements in the stem of the adult Cuscuta renders 

 a large development of tracheides in the haustorium of the parasite 

 superfluous. 



It sometimes happens that the epidermis, beside the connecting 

 haustorium of the two branches, presents a very peculiar appearance. 

 It is well known that where the branch of Cuscuta lies in contact 

 with its host the epidermal cells assume a columnar foiin. "Where 

 the two branches of the parasite come into contact the columnar epi- 

 dermis may be formed on each. The outer ends of the epidermal cells 

 of both become pointed, and the two epidermises interlock together, 

 so as to form what appears in section a single tissue two cells deep. 



"When stained this tissue stands out markedly from the other 

 tissues of the branches, not only owing to the shape of the cells, but 

 also on account of the different structure of its nuclei. The nuclei of 

 the other tissues are large when compared with those of other flower- 

 ing plants, and are very rich in chromatin, and consequently stain 

 vigorously with blue dyes. The nuclei of the interlocking epidermises 

 become relatively enormous and almost fill the whole cell ; the blue- 

 staining elements are relatively reduced, while many red-staining 

 bodies (nucleoli) are seen within the nuclear membrane. 



