Physiology of the Genus Cuscuta. 55 
From the time of Palm 1 and Von Mohl 2 , who studied 
certain species of Cuscuta in the course of their investigations 
on climbing plants in general, these interesting parasites have 
been so much studied and written about that, for the sake of 
a tolerably complete presentation of the new observations 
which I have to communicate, I must repeat much that is 
generally known. The student of the plants of this genus 
is especially indebted to the papers of Ludwig Koch 3 , and to 
the second of these I shall have frequent occasion to refer. 
In this paper I shall consider first the formation of the 
haustoria, the conditions necessary for this and for their full 
development, the general relations of the parasite to its 
environment ; and second the penetration of the haustoria into 
the host. 
I. The Formation of Haustoria. 
1. Germination and early grozvth . 
If the seeds of one of the three species of Cuscuta above 
mentioned be sown on moist earth, they gradually absorb 
sufficient water to double their size, and, in eight or ten days, 
germinate, pushing through the integuments of the seeds 
roots which are snowy white in colour. Such a root, short, 
thick, more or less spindle-shaped, devoid of a cap, and 
with short, though rather numerous hairs (their length varies 
directly with the amount of moisture), is very feebly geotropic 
and penetrates the subjacent soil for only one or two milli- 
metres, if at all. Instead of the cells of its central cylinder 
differentiating into vascular bundles, which are at first radial 
and separate, later, through secondary thickening, becoming 
collateral and confluent, the central cylinder consists of no 
lignified cells at all ; the walls remain thin, and, though the 
1 Palm, L. H., Ueber das Winden der Pflanzen, Stuttgart, 1827. 
2 Mohl, H. v., Ueber den Bau und das Winden der Ranken und Schlingpflanzen, 
Tubingen, 1827. 
3 Koch, L., Untersuchungen liber die Entwickelung der Cuscuteen, Hanstein’s 
Bdtanische Abhandlungen, Bd. II, Heft 3, 1874; Die Klee- und Flachsseide, 
Heidelberg, 1880. 
