92 
Peirce . — A Contribution to the 
steep spirals ; for the number of turns within a short distance 
and the considerably larger diameter of the stem, as well as 
its being firmly attached to the host by the haustoria, ensure 
a degree of stability and permanence unattainable in other 
parts. After the haustoria formed on the close spirals have 
penetrated, that part of the stem loosely twined in a steep 
spiral around the host which intervenes between two adjacent 
groups of haustoria, acts merely as a conductor of food from 
one part to another. It is no longer of mechanical advantage 
to the plant, and it therefore soon ceases to grow. Indeed, 
so slight and so unimportant does the physiological work of 
conduction eventually become, when no flowers are borne on 
the intermediate portions of the stem, that they sometimes 
atrophy and entirely disappear, leaving isolated the short, 
close spirals bearing clusters of flowers. It is plain, therefore, 
that the alternating regions of sensitiveness and insensitive- 
ness which are so important in their almost totally distinct 
ways during the period of active vegetation, continue to be 
distinct in habits and in importance in the reproductive stage. 
The unirritable parts were of use in distributing the parasite 
over as much of its host as possible, and often also in reaching 
new hosts from which food might at the same time be drawn : 
the irritable parts fixed the parasite at many points in the 
wide area won by the rapidly-growing insensitive parts, and 
at these points developed the haustoria. As repeatedly 
proved by the experiment of simply severing or of entirely 
removing the stem between two such regions of haustorial 
formation, after the haustoria have well penetrated into the 
host, its further use, even at such early stages in the plant’s 
history, is comparatively trifling. That even in nature the 
removal of these intermediate segments sometimes takes 
place, shows how independent of each other the haustorial 
segments are. One can, by dividing a plant in each of these 
intermediate regions, produce a number of individuals whose 
yield of seeds will be as good in quality and quantity as that 
of undivided plants, provided of course all other conditions 
are equal. Indeed, it is also possible during the latter part of 
