320 Peirce . — -On the Structure of the Haustoria 
frequently. The branches grow either in the cambium-layer, 
or to the wood and bast. In the wood and bast (see Fig. IV, 
PL XV, red cells) the chains become broken and the cells 
isolated. The reason for this is simple. The cells which 
compose the chains found in the cambium, by their continued 
growth and division lengthen the chains. The cells which 
compose the branches running to the wood and bast do not 
long continue to grow, or to divide. Their neighbours do 
grow, however, and these branches, being in radial lines to and 
from the centre of the stem, are pulled apart by this growth. 
The process of isolation takes place most rapidly in the 
phloem, for reasons which will be given presently. These cells 
grow and multiply in the cambium ; they grow only slowly, 
and do not multiply, in the wood and bast. 
If now a cross-section of a Cissus - root be made through 
one of the larger, more or less hemispherical swellings that 
are found at irregular intervals on its surface, one sees a 
structure similar to that shown in red in Fig. VI, PI. XV. An 
examination shows that it is composed of a great number of 
cells, the majority of which are exactly like those just 
described. These swellings are the more or less advanced 
stages in the development of the floral structures of 
Brugmansia. As already shown by Graf zu Solms-Laubach 1 , 
they are formed by the multiplication, at certain points, of the 
cells which compose the chains above described. This is 
clearly shown in P'ig. I, PI. XIV, where part of a young bud 
is connected with a branch of one of these chains penetrating 
the phloem of the adjacent bundle. The formation of a 
floral structure begins in the interfascicular cambium adjacent 
to a bundle, as shown in Fig. V, PL XV. The multiplication 
of the cells which compose the chain takes place at first more 
rapidly on the side toward the centre of the stem, forming a 
more or less conical structure composed entirely of thin- 
walled parenchyma-cells, rich in protoplasm, rather dark 
brown in colour. This structure is rather closely applied to 
1 Die Entwickelung der Bliithe bei Brugmansia Zippelii, Botanische Zeitung, 
1876. 
