ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
213 
crcnic, apocrenie, ulmic, and liumic acids, ulinin, and humin. Of these, 
the first two are soluble in water, the third and fourth in alkalized 
water, the last two altogether insoluble. The humus affects not only 
the chemical, but also the physical properties of the soil, rendering it 
looser and capable of containing a larger quantity of water. In soil 
containing humus, plants develope a very much more abundant root- 
system. The roots are able also to penetrate organic substances, such as 
leaves, bark, wood, &c., and to obtain nutriment from them. A few chloro- 
phyllaceous plants, e.g. Melampyrum pratense and Pedicularis palustris , 
possess on their roots special organs — haustoria — which unite in their 
growth with the organic substances in the soil, and extract nutriment 
from them. While they are true parasites, they appear to depend mainly 
on saprophytism for their nutrition. It is only in soil containing 
humus that the mycorhiza-fungus can develope. 
Of the plants with true roots examined, the following were found to 
be more or less invested by a symbiotic fungus-mycele : — Orchis maculata , 
Platanthera bifolia, and Epipactis latifolia (endotrophic with rudimentary 
root-hairs), Betula pubescens (ectotrophic, no root-hairs), Lysimachia 
vulgaris (endotrophic, a few root-hairs), Monotropa hypopitys (ectotrophic, 
no root-hairs), Ledum palustre and Andromeda polifolia (endotrophic, no 
root-hairs), Helichrysum arenarium (endotrophic, a few root-hairs), Epilo- 
bium palustre and angustifolium and Geum rivale (endotrophic, no root- 
hairs. 
Bleeding of Plants.* — Dr. A. Wieler discusses in great detail the 
phenomena connected with the bleeding of plants, understanding by this 
term not only a flow of sap as a consequence of injury, but any escape of 
water from a cell, including therefore the trickling of drops from leaves 
and from fungi, and the secretion of digestive glands. The author 
argues, from the results of a great variety of observations, that bleeding 
is a function of special cells, and is manifested when there is an unequal 
osmotic pressure on the opposite sides of the protoplast of one of these 
cells. It cannot take place without oxygen, and may be assisted by im- 
bibition. In most trees the phenomenon exhibits an annual periodicity, 
though this is not always the case ; and the facts with regard to a diurnal 
periodicity vary greatly in different plants, and even with the same 
species under different conditions, especially as regards the age of the 
individual. The escape of the fluid from the digestive glands of insec- 
tivorous plants is dependent on exosmose. 
Reserves of Water in Plants. f — M. A. Prunet has investigated this 
subject in the case of a large number of plants, woody, herbaceous, and 
climbing, especially in relation to the comparative amount of water in 
the nodes and internodes. He finds that, as a general rule, the nodes 
of dicotyledonous plants contain a reserve of water capable of reme- 
dying, to a certain extent, sudden ruptures of equilibrium between 
the direct supply through the foliar bundles and the loss by transpi- 
ration ; the structure of the nodal tissues is such that the cauline 
bundles can generally replace the foliar bundles when the supply 
* Beitr. z. Biol. d. Pflanzen (Cohn), vi. (1892) pp. 1-211. 
t Bull. Soc. d’Hist. Nat. Toulouse, xxv. (1891) pp. 33-70. Cf. this Journal, 
1892, p. 60. 
