ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
83 
tho parasite of a solvent which attacks aud dissolves, first the epidermal 
and then the underlying cortical cells of the host. The haustoria are 
arranged in groups along the stem. From a morphological point of 
view the haustorium of Cuscuta is a lateral root, which developes into a 
structure, the bicollateral vascular bundles of which are united with the 
vascular bundles of the host by two strands of tracheids, and two strands 
of sieve-tubes and their companion-cells. Its xylem and phloem unite 
directly with the xylem and phloem of one Or more bundles of the host ; 
and an unbroken connection exists between the conducting tissues of the 
parasite and its host. The growing point of the haustorium is covered 
by a single layer of cells, which the author terms collectively tho 
“ sucker.” 
The structure and development of the haustoria in the other three 
species of Cuscuta examined differ in no essential respect from those of 
C. americana. 
After the comparatively small amount of food stored in their seeds 
is consumed, the species of Cuscuta are absolutely dependent upon their 
hosts for food ; and it is through the sieve-tubes in the haustoria, and 
their direct union with the sieve-tubes of the host, that the parasite 
obtains from it its elaborated substances and reserve food-materials. 
Comparing these results with those obtained in other phanerogamic 
parasites, the author states that in those which do not contain chloro- 
phyll (species ol Kafflesiacem and Balanophorese) the structure of the haus- 
toria is the same $ they obtain the whole of their nutriment through the 
connection of their sieve-tubes with those of their host. In the mistle- 
toe, on the contrary, the haustoria contain no sieve-tubes. It is a 
“ water parasite,” its host performing for it only the functions of a root, 
— absorption, conduction, and mechanical support. 
Bulbils of Dioscoreaceae.* — M. C. Queva describes in detail the 
structure of the bulbils on the stem of Dioscorea Batatas and Helmia 
bulbifera. They are always the result of the growth of a hypertrophied 
axillary bud ; occasionally one will be the product of the concrescence of 
two buds. 
Tubers of Apios tuberosa and Helianthus tuberosus.f — M. Nypels 
has examined the structure and development of the tubers in those 
plants, and states that in both their formation is mainly due to the 
closing of the non-differentiated elements of the central bundle, i.e. of 
the primitive central fibres and of the pericycle, secondarily also to the 
closing of the cortical parenchyme. The result is a hypertrophy of the 
cells of the pith, and a production of secondary parenchyme. 
Development of Arachis.J — M. A. Andouard describes the little- 
known bacterial tubercles in the root of Arachis hypogsea. All the parts 
of the plant contain a sugar, which appears to be exclusively saccharose, 
the largest proportion being in the root and stem. This is associated 
with starch, proteinaceous substances, oily substances, and pectic prin 
ciples. 
* Comptes Rendus, cxvii. (1893) pp. 316-8. 
f Bull. Soc. R. Bot. Belgique, xxxi. (1893) pp. 216-30 (2 pis.). 
X Comptes Rendus, cxvii. (1893) pp. 298-300. 
G 2 
