Ti i ie Os eal a i el ae ee 
19 
was not till the generating cells were resorbed that the gonidia lay 
loose among the other tissue. 
These researches by Tulasne and Nylander as to the origin of 
the gonidia were in neither case entered upon from any doubt as 
to the complete unity of the Lichen thallus, for at that time 
Lichens were taken by everyone without question to be what they 
seemed— simple autonomous plants, just as much as a daisy or an 
oak. It was not till rather more than twenty years ago that any 
doubt whatever was thrown on this belief, or that the teaching of 
Tulasne and Nylander was challenged. 
To understand the reason which led to the assertion of a dual 
nature in Lichens, we must refer to certain differences among the 
gonidia themselves. Not only do they occupy, as we have seen, 
different positions in the thallus, but there are other differences of 
moment between the gonidia of one plant and those of another. 
These differences are in respect to the character of their cell wall, 
the colour of their contents, and their mode of division and aggre- 
gation. Dr. Nylander has carefully studied them with regard to 
all these points, and classified the different forms that occur, 
giving to each distinctive names. I do not purpose to trouble you 
with these distinctions, as it would occupy too long. It is only 
necessary to remember that gonidia do differ to some considerable 
extent in different species of Lichens. 
Well, rather more than twenty years ago, Professor Schwendener, 
a German botanist, began to study the thallus of Lichens, and, in 
two out of three parts of the work in which he gave to the world 
the result of his investigations, he represented the gonidia as growing 
in natural and orderly course out of the other tissue, and described 
and figured the way in which he conceived them to arise from the 
other thalline cells. 
About this time Schwendener’s attention seems to have been 
drawn to the great resemblance some gonidia bore to organisms 
known as uni-cellular Algee or Protophytes, which lead an appar- 
ently free and independent life on moist rocks, earth, and the bark 
of trees. He then suddenly and completely changed his views, 
and asserted that he had never had any reason to believe that the 
