74 
Peirce. — A Contribution to the 
of the stem with the host on either side. To put the question 
directly — Is each haustorium induced by contact immediately 
over its point of origin, or can haustoria be induced to form 
between two points by contact at these two points only? 
The question may readily be answered by marking the growing 
and twining stem with Indian ink at the last points of contact 
with the host, and bringing against it. at a distance of one 
centimetre or less, either another host or a rod of suitable 
size. When the Cuscuta has made one or two close turns 
about the support, it will be noticed that the dots which were 
over the last points of contact with the host have now been 
brought by growth into the region intervening between the 
host and the new support, and that when haustoria appear 
there they form at or behind those points, not in front of 
them and towards the tip, and somewhat earlier than those 
on the part of the parasite which is in contact with the new 
support. If they were induced between the points of contact, 
no contact having ever existed in the region of their origin, 
they should appear at the same time as or later than those 
against the support. Their earlier appearance and the change 
of position of the dots make it quite evident that they are the 
results of contact at the points where they originate and that 
their abortion is due to the contact being only temporary. 
Each haustorium is, therefore, the result of irritation produced 
by contact at the place where it forms. 
I said above that contact alone, though sufficient to induce 
the formation of haustoria and to cause some changes in the 
overlying epidermal ceils if continued long enough, is not 
sufficient to secure the full development of haustoria or to 
produce extended changes in the epidermal cells. It has 
often been observed that when a branch of a Cuscuta has 
wound itself in a close spiral about a rod of glass or wood 
that, though the haustoria are formed, as shown by the 
swellings on the concave side of the stem, and also by sections, 
they do not develop very far. Sections show further that, 
though the epidermal cells at the points of contact and over- 
lying the nascent haustoria do elongate slightly, no such 
