30 STUDIES IN ROOT-PARASITISM. 
An examination of the diagrams on Plate IX will show that 
in the haustoria examined there is no great development of 
secondary thickening (see for instance the case of Santalum in 
Santalum, Part II, Plate LX) and, from the frequent clearness of 
the tissues in the older stages, it is probable that the life of these 
organs is comparatively short. A certain number of references 
to the age of haustoria are scattered through the literature. on 
root-parasites. Thus Granel’ remarks that the haustoria even 
of perennials do not usually last longer than one year. Leclere 
du Sablon’? noted that older plants of Pediculams form new 
suckers each year. Heinricher’ showed that the haustoria of 
Lathrea can live for more than a year and asserts that Krause 
has proved the same for Bartschia alpina. Kusano, in his studies 
of the haustoria of Buckleya Quadriala in Japan, speaks of the 
growth of the haustorium keeping pace with that of the 
root to which it is attached, and of haustorium and root growing 
thus together for as many as a dozen years with cambiums in 
contact. In the tropies we have no means of determining the 
age of haustoria by means of annual rings as did Kusano, for 
these are not developed with any distinctness. But we have, on 
the other hand, some reason to believe that the activity of the 
haustoria is short-lived, because of the regular decay of the 
vascular system at a certain point, the interrupted zone. On the 
whole one is led to believe, from the haustoria so far examined, 
that the functional activity of haustoria in the Santalacee and 
Olacacee in the tropics is not long continued, may indeed cease 
long before the actual growth of the haustorium does. 
In older haustoria of Santalum, where much secondary 
thickening has taken place, it was noted that the inner layers of 
secondary wood in the axis became discoloured and filled with 
gum, the protoxylem, curiously enough, not suffering this change 
| Granel, Note sur l’Origin des sugoirs de quelques Phanerogames Parasites. Bull. 
d. 1. Soc. Bot. de Fr. XXXIV, 2. IX. 313—321. 1887. 
2 Leclere du Sablon, ib. 
8 E. Heinricher, Die griinen Halb-schmarotzer. II]. Bartschia und Tozzia. Jahrb. 
f. wiss. Bot. XXXVI, 665—752. 1901. 
