NUTRITION 
Among the many thousand species of heterotrophic plants, the bac- 
teria and fungi hold the dominant place. A few seed plants lack 
chlorophyll entirely, such as the Indian pipe (Monotropa), beech drops 
(Epifagus virginiana), dodder (Cuscuta), etc.; and some have only par- 
tially lost it, or with a good supply nevertheless have the nutritive habits 
of the non-green plants. 
The families in which such dependent species are prominent are theLoranthaceae, 
Rafflesiaceae, Scrophulariaceae, Orobanchaceae, and Balanophoraceae. 
If a plant cannot make carbohydrates, it must of necessity get food 
directly or indirectly from some plant that can. The direct way of 
doing this is to live on or in a live green plant. The indirect way differs 
only in that the food secured is more remote from the original food 
maker. Thus, a plant may live upon or in some animal or some non- 
green plant, or upon the dead bodies of these, more or less decayed and 
disintegrated. Indeed, decay and disintegration are only the obvious 
evidence that plants (chiefly the minute bacteria and fungi) are living 
upon such a dead body. And not infrequently 
death itself is simply the result of the vigorous 
development of such creatures on or in the 
body of a once healthy organism. 
Parasitism. An association between two 
live organisms is known as symbiosis. When 
one obtains its food from the other, the rela- 
tion is called parasitism, and the two are known 
respectively as parasite and host. As a rule 
the food maker is called the host, and the other 
the parasite; if neither or both be food makers, 
the larger is distinguished as the host. Thus, 
fungi are parasitic on leaves or twigs or in 
the wood of trees, or on animals; " beech- 
drops " (Epifagus virginiana, a small flower- 
ing plant) is parasitic on the roots of the beech 
tree; mistletoe is parasitic on elms, etc. This 
relation requires the closest contact between 
the cells of parasite and host, and the parasite 
even penetrates the cells of the host in many 
cases. The smaller parasites, such as fungi, 
FIG. 651. An epidermal 
cell of a grass (Poo) penetrated 
by a branched haustorium (h) 
of a fungus (Erysiphe grami- 
nis) ; the mycelial hypha to 
which the slender penetrating 
tube (a) is attached is not 
may grow bodily through cells, doubtless dis- shown. After SMITH. 
