1074 Stephens. — The Structure and Development of the 
can make its way through the cortex of the maize, and, once the endodermis 
is passed, into the comparatively slightly lignified vessels of the young root. 
Here it is interesting to note that several haustoria were found trying to 
penetrate an unknown dicotyledonous root which possessed a layer of cork 
about six cells thick round the stele. The haustoria had entered the root 
as far as the cork, and were striving to penetrate it with the secretion of 
much ferment, but they had not got half-way through. Though they had 
grown to the size of the haustorium of Fig. 6, the axial strand of tracheides 
had not yet been formed, confirming the opinion stated above that this 
is only formed after the haustorium has penetrated to the stele of the host. 1 
In this case, a line of 4 crushed tissue 5 had been formed down the centre of 
the ‘ nucleus \ 
The chief interest of this investigation lies in the exactitude with which 
the origin and development of the haustoria can be followed up through the 
transparent tissues of the mother root, and in the light which is thus thrown 
on the disputed question of whether haustoria are to be regarded as organs 
sui generis or as much modified lateral roots, a point on which investigators 
have differed even in regard to the same species. 2 My first-hand know- 
ledge of the literature of parasitism is not sufficient to enable me to add to 
the many discussions 3 on this point, beyond recording the fact that in 
Striga all the lateral haustoria are clearly exogenous in origin, and show no 
homologies with the lateral roots. Very rarely a case is found in which the 
tip of a Striga root has apparently met a maize root and formed a terminal 
haustorium. I use the word * apparently ’ because in every such case but 
two a new growing point had been formed near the apex of the haustorium 
(as is described for like cases in Santalum , 4 Exocarpus , 5 and Krameria 6 ). 
When this new root had grown on, the haustorium would present the 
appearance of an ordinary lateral one ; but it seemed clear in the half-dozen 
cases seen that the haustorium was originally terminal. It might of course 
still have had an exogenous origin from one of the layers of the very simple 
root-tip, but the appearance of the haustorium would suggest that the cells 
of the root-tip simply grew out as papillae into the host, the vessels extended 
down to form the central strand of the haustorium, and the inner cortical 
cells divided up to form the 6 nucleus \ Unfortunately, no young stages in 
the development of such a haustorium have been seen. It may be noted 
that these haustoria were all formed at the ends of fairly long roots ; it 
might have been expected that in the case of two roots running parallel, 
as in Fig. i, penetration by the lateral roots of the haustorium might occur, 
but no such case was found. 
1 Fraysse (’06) remarks of the haustoria of Osyris alba (p. 28 ) : ‘ Dans aucun cas, l’appareil 
vasculaire n’apparait completement forme avant ^installation definitive du parasite. Des que la 
penetration est suffisante, les trachees se difftfrencient et s’insinuent jusqu’aux divers vaisseaux . . . ’ 
2 Fraysse (’06), p. 23 . 3 Peirce (’93 and ’05), Goebel (’05), Fraysse (’06), & c. 
4 Barber (’06). 5 Benson (’10). 6 Cannon (’10). 
