BOTANICAL EVOLUTION. A419 
ment than the production of tendrils. Twiners as a rule produce 
about half as much stem again as tendril bearers. Thus, according 
to Prof. Asa Gray, a pea plant standing two feet high was found to be 
hardly more than two feet long, while a french bean of the same 
height was found to be three feet long. Again, tendril bearers can, 
from their first growth, climb along the outer branches of any neigh- 
bouring bush, and are thus fully exposed to the light, while twiners, 
from having to ascend bare stems, have generally to start their growth 
in the shade. 
One of the most singular developments which certain plants have 
undergone, is that of becoming parasites, but, as I shall show you, we 
can sec, in many cases, how this habit has been arrived at. In a 
_ naturally damp forest, such as that of this colony, the accumulations 
of fallen leaves, twigs, and similar materials on the trunks of trees, 
form suitable localities for the growth of many small plants, and so we 
find often a perfect colony of young plants growing on the stem of some 
older one. In this way, no doubt, arose that class of plants of which 
we have so many examples in New Zealand, true epiphytes, or 
plants which grow on other plants, but without taking any nourish- 
ment from them. We have, for example, some five species of 
epiphytic orchids, which grow on stems of trees or bare rocks, and 
which depend for their food solely on the carbonic acid and moisture 
of the air. Their roots are true aerial roots, and not only do not 
require soil, but actually rot away if covered with soil. But there are 
many others which require a little soil, and from this latter class, 
apparently, some forms of parasites have originated. But further to 
understand the beginning of parasitism, we have to remember that 
there exists in plants a sort of natural power of grafting. Thus two 
young trees sometimes become crushed together. At the place where 
the stems are in contact complete union of the tissue may take place, 
and the two stems amaleamate. Such examples must be familiar to 
all. You may also have noticed a form of incipient parasitism that is 
by no means uncommon in our bush. Our broadleaf (Griselinia 
lucida) appears to have a faculty for growing on the stems of other 
plants, and it is a very common occurrence to see young plants of it 
growing on the rubbish accumulated on the stems of other trees. 
But frequently these young plants manage to put their roots through 
the bark of their host, and when this is accomplished, they grow 
exactly like grafts. Such natural grafts are manifestly parasites, and 
it is most probable that in this way the parasitic family of mistletoas 
originated. From the great differentiation which mistletoes have . 
undergone, and their extensive geoeraphical range, it would seem 
that the order is one of considerable antiquity, and it would be a most 
interesting research to try and work out their origin. They are 
abundant in the tropics and range into the temperate regions. They 
are nearly all dependent upon birds for their dissemination, as these 
eat the fruit and drop the seeds on trees: These seeds—which will 
‘not grow in soil—send their first root at once into the bark of the tree 
on which they fall, and this incorporates itself so completely with the 
wood that it is difficult to find any line of demarcation between the 
parasite and its host. It is worthy of note that mistletoes are 
furnished with ordinary leaves, and this is necessary, because from 
the depth to which they incorporate themselves with their host, the 
