152 Boeshore — The Morphological Continuity of 



As a still more condensed type Christisonia might well come 

 next to Aphyllon. This is described and figured by Worsdell 

 (20, p. 134). He describes three species of Christisonia, but 

 the one that concerns us here is Christisonia subacaulis. To 

 quote from him regarding it: "the most abnormal feature oc- 

 curring in these plants is presented by the subterranean portion 

 of Christisonia subacaulis especially, which, on investigation, 

 is discovered to consist of organs having the character of roots, 

 though their morphological nature is well concealed, owing to 

 their extreme modification arising from their parasitic habit 

 . . . The tubers, which arise at intervals in the root system 

 of the plant just named, are the most important parts of it, for 

 it is from these that the haustoria are chiefly formed, while they 

 also act as reservoirs of nutriment for the whole plant . . . 

 The haustorium is interesting as having an exogenous origin, 

 and not an endogenous one, as described for many other para- 

 sites; it agrees in this respect with that of Rhinanthus." 



The roots of Epiphegus are shorter than the roots of Aphyllon 

 and seem to have lost all parasitic power, this function being 

 accomplished by the tuberous swelling. A transverse section 

 of such shows the host root deeply or shallowly buried within 

 the tissues of the tuber and thus connection is established be- 

 tween the two. In these degradation stages the tissues of the 

 parasite have become correspondingly more simplified as demon- 

 strated by Cooke and Schively (17). 



In Conopholis (Plate XVI, Fig. 32) no external roots are visi- 

 ble. With the more complete and highly specialized paras- 

 itism has come a complete absorption of roots, or they may be 

 represented by a large mass of stone cells, but wholly buried 

 within the enormous swelling on the oak roots. One specimen 

 was found which measured 10 inches in length and 6 inches 

 across. Sections were made of smaller specimens but these 

 only showed masses of stone cells. All trace of definite systems 

 seem to have been lost. And so, Conopholis well represents, 

 both morphologically and physiologically, the climax of the en- 

 tire group. 



In summing up the discussion on roots it can be said that, be- 

 ginning with G. flava and ending with the genus Lathraea, a 

 gradual condensation in extent of root system is accompanied 

 by a gradual degradation of root tissues which in Lathraea be- 



