1073 
Haustorium of Striga lutea . 
cortex of the stem, and that the tracheides, lacking the definite point of 
development afforded by the vascular system of the root, run in scattered 
lines through the f nucleus ’ instead of in a central strand. The ‘ nucleus ’ 
seems to grow backwards through the stem, and the lines of tracheides run 
back with it till they meet and link on to the vessels of a leaf-trace. If 
they do not meet a leaf-trace, they simply end blindly in the ‘ nucleus ’. 
( d ) Mechanism of Nutrition. 
The whole question of the nutrition of this parasite, especially during 
the underground portion of its life-history, is obscure. While the water- 
carrying vessels of host and parasite are connected so as to allow of a free 
passage of water and salts, there is no such conducting system for assimilated 
food. No sieve-tubes are formed in the haustorium, none have been found 
in the mother roots, and there is apparently no connexion with the phloem 
of the host. It is of course possible that the parasite may absorb food by 
osmosis from the sieve-tubes of the host where its thin-walled cells come 
in contact with these, as is suggested by Peirce 1 for Arceuthobium occi- 
dentale. But as the haustoria fasten only upon the younger roots of the 
maize, in which the sieve-tubes are not easily distinguished or have not 
yet been formed, I have not been able to ascertain whether the conditions 
for such a transference are found here. Until the subaerial shoot is formed, 
the plant thus apparently has to depend for its supply of assimilated food 
on the reserve stores passed over from the phloem to the xylem of the 
host, and on what the haustoria may absorb from the cells dissolved by 
its ferment. Many microchemical tests have been made to find out what 
food-stuffs are transferred from host to parasite, but without result. There 
is no storage, even temporary, of food such as has been recorded for the 
haustoria of other parasites 2 — a fact which may be connected with the 
relatively short life of the haustorium in this case. It is not known just 
how long an individual haustorium may live, but the fact that they are 
never seen on the older roots of the full-grown maize shows that their life 
is not a long one. 
Discussion. 
The fact that the haustorium of Striga may be regarded as compara- 
tively simple in structure has already been noted. No glands are formed to 
assist in penetration ; 3 there are no arrangements of strengthening tissue ; 4 
and no ‘ collapsed layers’ are seen, such as are generally found in haustoria 
which have to penetrate the woody cylinder of dicotyledonous roots. All these 
facts may be correlated with the comparative ease with which the haustorium 
1 Peirce (’05), p. 109. 2 e. g. Barber (’06), Fraysse (’06), Benson (’10), &c. 
3 As formed in, e. g., Santalum album (Barber, ’06). 
4 As seen in, e. g., Osyris alba (Fraysse, ’06) and Krameria canescens (Cannon, ’10). 
