134 
riance and exhaust their vital juices. The gardener 
who has been too profuse of seed must thin out the 
young plants of cabbages, lettuces, carrots, &c. if he 
hopes to obtain vigorous plants. He prunes redun- 
dant shoots, and suffers not more than a limited 
number of fruits to ripen on a branch. ‘Trees in 
thick forests weaken the growth one of another. 
They are said to be drawn upward. They become 
tall and slender, without side branches. Their close 
meeting summits exclude sunshine from their roots. 
The impediment to evaporation converts the soil to 
a watery bog, too loose to afford a firm basis for 
their roots. In such condition storms lay prostrate 
large tracts covered with timber, destined in time 
to become peat moss. Some forests are called tole- 
rant, when the lofty trees allow underwood to grow 
beneath them, as oaks. Some are called intolerant, 
beneath which inferior plants wither and_ perish, 
as pines. Innumerable climbing plants and para- 
sites affect forests, meadows, and corn-fields. The 
descriptions of Brazilian forests in many late publi- 
cations render detail needless of the lianes, or 
climbers, which obstruct all progress through them 
without laborious use of the axe. Tares overwhelm 
wheat and barley crops. Dodder is often oppressive 
to beans;—ivy to our forest timber. The rhizo- 
morpha creeps under the bark of aged trees, and 
hastens their decay. Fungi, called false parasites, 
destroy leaves and roots. Lichens and mosses in- 
jure timber by attracting moisture to the bark, and 
affording a lodgement for insects. 
