70 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
are Leguminosre and Composite. With the exception that some hosts 
seem more favourable to the growth of the parasite than others, the 
same species of Orobanche growing on different host-plants presents no 
perceptible difference of any kind. On the other hand, they inflict 
great injury on many cultivated crops, especially hemp, clover, and 
tobacco. 
Phanerogamic Parasites.* — Dr. F. Johow gives a summary of all 
that is at present known with regard to parasitic flowering plants, 
which he classifies under four heads, viz. : — Euphytoids, which 
have developed from ordinary terrestrial autotrophous plants (Loran- 
thacese, most Santalacere, Rhinantheae, Orobancheae, &c.) ; (2) Lianoids, 
developed from climbing plants ( Cuscuta, Cassytha) ; (3) Epiphytoids, 
those that resemble epiphytes except in their parasitic habit (Loran- 
thaceae, some Santalaceae) ; (4) Fungoids, which present no relationship 
with any autotrophous group (Balanophoraceae, Cytinaceae). Each of 
these classes, except the last, may be again divided into Holoparasites 
and Hemiparasites. Some again are obligatory, and others facultative 
parasites. The total number of species known is somewhat over a 
thousand, of which about one-half belong to the Loranthaceae. 
As regards the choice of a host, some species grow only on a single 
host-species, as Loranthus aphyllus on Cereus peruvianus, Cuscuta Epilinum 
on the flax ; others only on different species of the same genus ; others 
only on different genera of the same family ; while others again have 
no such restrictions. Some again choose in preference different hosts in 
different districts ; thus, for example, the mistletoe grows in some 
regions almost exclusively on the apple, in others on the pine ; Arceu- 
thobium Oxycedri only on Juniperus Oxycedri in Europe; in North 
America on different species of Pinus. Many parasites confine their 
attacks to special parts of the host-plant ; as the Loranthaceae entirely 
to branches, the Balanophoraceae entirely to roots. The organ for the 
absorption of nutriment is, in all except the Cytinaceae, differenti- 
ated haustoria, which are apparently, from a morphological point of 
view, metamorphosed roots. In the Cytinaceae the entire vegetative 
structure of the parasite, imbedded in the interior of the host, serves as 
a haustorium. 
A special description is also given of the mode of parasitism in the 
different groups ; and the species or genera belonging to each are 
enumerated. 
Rooting of Bulbs and Geotropism.f — M. H. Devaux states that the 
anomalous method of rooting by means of stalked bulbs in the common 
tulip has been observed by Germain de Saint Pierre, Irmisch, and Royer. 
But this method of rooting is not confined to the tulip. In various 
species of Allium , Muscari, Scilla, Hyacinthus , Calystegia , Sagittaria , 
Tamus , &c., one or more internodes of the stem may become enlarged, 
and thrust vertically into the ground by their free extremity ; this 
extremity bears a bud which is destined to be transformed into a bulb or 
tubercle. '1 his phenomenon appears to be the result of geotropism. 
* Verhandl. Deutsch. Wissensch. Ver. Santiago, ii. (1890) pp. 68-105 (10 figs.), 
t Bull. Soc. Bot. France, xxxvii. (1890) pp. 155-9. 
