8o 
Peirce. — A Contribution to the 
growth is expended in penetrating the host. The haustoria 
formed by the cuttings, on the other hand, not having in the 
comparatively slender curved stems a rigid base against which 
to press and thus to make all the force produced by their 
growth tell in the penetration of the host, push the parasite 
away from the host, thus wasting force and increasing the 
distance through which they must grow in order to reach the 
conducting tissues of the foster-plant. 
Still another difference between these two is also evident, 
namely, in their colour. The colour of the unsevered branches 
resembles that of the rest of the plant, varying from a straw- 
yellow to a decided orange, according to the nourishment and 
illumination which they receive. Ill-nourished and therefore 
thin plants are pale, no matter how well illuminated ; but the 
better the illumination which well-nourished plants receive, 
the more intense becomes the colour. The colouring-matter 
is situated in small chromoplastids, orange in hue, which the 
cells of the central cylinder contain in much larger numbers 
than those of the peripheral layers. With the ordinary 
microscope no chlorophyll-granules can be distinguished, 
though the presence of chlorophyll, as previously stated, has 
been shown by Temme by micro-spectroscopic methods. In 
and about the flower-clusters of all the species of Cuscuta 
which have come under my observation there is always an 
amount of chlorophyll sufficient to be recognized by the 
microscope, and often these parts are decidedly green. 
Turning now to the cuttings, one sees that, though they 
may have been deep orange in colour when cut, the colour 
has begun to change before twenty-four hours have expired, 
and within forty-eight hours they have become distinctly 
green. C. europaea changes more slowly than the other two 
species, yet this plant too becomes green within two days after 
cutting. Longitudinal sections show plainly that many chloro- 
phyll-granules of very considerable size have been developed, 
and that their distribution is the reverse of that of the chromo- 
plastids above mentioned, since they are much more abundant 
in the cortical parenchyma than in the central cylinder. Their 
