656 Thoday.—On the Histological Relations between 
various hosts were also studied ; of these Cuscuta europaea on the Hop, 
Cuscuta reflexa on Begonia and Ficus , and an unnamed variety growing 
on Solidago were not found to be very useful; the best material was 
obtained from Cuscuta europaea growing on Vitis, and Cuscuta reflexa 
growing on Salvia sp. The former, growing out of doors in the Cambridge 
University Botanic Garden, was collected in July and October,the latter in. 
June and July from a plant growing in the greenhouse. 
Most of the more important results were obtained from Cuscuta reflexa, 
a perennial species growing on Salvia , and as the histology of the phloem 
in the latter genus had not been studied, it became necessary in the course 
of the work to make some investigations on its sieve tubes ; these are 
recorded in the first part of the paper, while the second part deals with 
the histology of the parasite Cuscuta , particularly with the development of 
its sieve tubes. The investigation of the phloem of these two plants is of 
some interest in itself, since it is the first time that the phloem of so small 
a plant as Salvia or that of a parasite has been studied by recent methods. 
In the third part, which is of more interest to the general reader, an attempt 
is made to give some account of the manner in which the haustorium pene¬ 
trates the host, and deals especially with the origin of the sieve tubes in the 
haustorium and the development of connexions with the sieve tubes of 
the host. The facts brought to light afford important evidence both on 
the value of sieve tubes for conduction, and on the efficiency of sieve 
plates ; the paper closes with a short discussion of these matters, and of 
the conflicting theories concerning the nature and origin of connecting 
threads. 
I am indebted to Mr. Lynch for kindly aiding me in obtaining material. 
The work for this paper was begun in the laboratory of the Royal Holloway 
College, but was chiefly carried out at the Botany School, Cambridge, while 
holding a Fellowship at Newnham College. 
Methods. 
The methods used for preservation and staining were based on those 
used by Gardiner, 1 Hill, 2 and the author 3 in previous work. The material 
found best for the minute histological work was preserved in a solution of 
0*5 gramme iodine in 0*75 gramme potassium iodide in 100 c.c. of distilled 
water. The results obtained by the safranin method without a wall stain 
were confirmed by a study of paraffin microtomed sections stained in 
ruthenium red, chlor-zinc-iodine, or Delafield’s haematoxylin ; in some 
cases the actual sections used for the examination of sieve plates, &c. (and 
stained in safranin, aniline blue, 4 and London blue), were afterwards placed 
in Delafield’s haematoxylin, so that the relations of the walls might be 
r Gardiner, 1898 a and b. 2 Hill, 1901 and 1908. 3 Sykes, 1908. 
4 Sykes, p. 298, 1 . c. [Water blue (Hofmann’s blue) made up with aniline.] 
