SYSTEMATIC POSITION OF MITRASTEMON. 207 



tubes caused by so-called " obliteration " (TscHiRCH p. 345) ; while the 

 secondary bast of the latter is not at all swollen, and there is present a 

 considerable amount of the depressed lamellae of sieve tubes. We also find 

 here that the swelling of the bast-tissue is especially large in the floral 

 polster. This is possibly ascribable to the same cause as that to which we 

 ascribe the similar effect in the case of galls (KEENER p. 472) and mycor- 

 rhiza (SfflBATA 1. c.) 



The intramatrical tissue, when fully grown, produces endogeneously a 

 flower-bud, which breaks up the bark of the host-root, and protrudes up- 

 wards a peduncle, just as in the case of a plant of the Rafflesiacese. (SoLMS- 

 LAUBACH I, p. 3 ; II., IV., LOTSY p. 833). 



2. Structure of the Peduncle. 



The peduncle of Mitrastcmon, as is usually the case with a parasite, is 

 extremely primitive in its anatomical structure. The tissue is formed by 

 nearly round parenchymatous cells which are largest towards the center of 

 the tissue mass and become gradually smaller towards the epiderm. Inter- 

 cellular spaces are greater towards the center and smaller towards the 

 periphery, and there are practically none at all outside of the ring of vascu- 

 lar bundles. The epiderm has no stoma. There are 5-10 horse-shoe shaped 

 or semi-circular, out ward- curving, vascular bundles around the central pith. 

 They are scattering when few in number, but come into close contact, when 

 there are many of them. Towards the epiderm on the outside of this 

 broken ring of vascular bundles, there are sometimes seen a very few small 

 bundles which seem to run into scales on the peduncles. There is generally 

 in the center of a bundle, in cross section, a group of a few spiral tracheids 

 arranged in a curved line, which is almost completely surrounded by layers 

 of plasmatic cells. The layer of plasmatic cells is thicker on the outer side 

 of the tracheidal bundles, than on the inner side. The cambium-layers, or 

 rather a few cambium-cells, are found just outside of, and close to, the 

 tracheidal-groups. The tracheidal cells here represent a primitive xylem, 

 and the surrounding plasraatic cells an as yet undifferentiated bast. I found, 



