9i 
Physiology of the Genus Cuscuta. 
longer irritable. The formation of haustoria, which depends 
upon irritability, which is itself dependent upon growth, is 
a process that takes place only during the period of active 
vegetation, or, in the case of C. europaea , after the period of 
maximum blooming is past and a second period of less active 
vegetation begins. From the time that active vegetative 
growth ceases and reproductive growth begins, all experi- 
mental study of the phenomena of the former must of necessity 
cease. I attempted by cutting off some of the young branches 
which were still being formed at the beginning of August on 
the plants in the Botanic Garden, and setting these as before 
described upon their appropriate hosts, to secure plants which 
would for a time at least continue to vegetate. All such 
efforts were futile. As soon as the cuttings had sent a suffi- 
cient number of haustoria (generally two sets were enough) 
into the hosts to secure an abundance of food, the buds 
already formed, and whatever new ones had in the meantime 
been formed, developed into flowers. Similar cuttings made 
in mid-October and set on Chrysanthemums growing in the 
greenhouse did not develop more than a few vegetative 
branches, though having an abundance of flowers. 
Chlorophyll may be plainly recognized in certain regions 
of the plants, at the reproductive stage, mainly in and 
about the flowers, as others have before stated ; but it is 
not abundant enough more than feebly to supplement the 
nutrition secured from the host. 
In the majority of the plants which I have observed, the 
largest and finest flower-clusters were situated in or very near 
regions on which haustoria abounded, that is, on the close 
spirals. The fewer clusters on the intermediate regions were 
markedly smaller in themselves, and the flowers which com- 
posed them did not attain the size common in others. The 
advantages of being near the immediate sources of food- 
supply are so evident that it is unnecessary to enumerate 
them : but there is a mechanical advantage also in the com- 
paratively heavy flower-clusters and the still heavier clusters 
of fruits being borne on the close rather than on the loose, 
