170 INTRODUCTION TO BOTANY 
Competition sometimes results in killing outright most of 
the competing plants; sometimes it only renders them dwarf- 
ish and incapable of producing many flowers or seeds. 
The means by which the successful individuals weaken or 
kill their neighbors are mainly 
1. Overshadowing, resulting in deficient photosynthesis in 
the shaded plants from lack of light. 
2. Robbing the defeated plants of water. 
3. Robbing them of soluble salts, such as nitrates and phos- 
phates of the soil. 
The deprivation 
of sufficient water 
and salts interferes 
with the nutrition 
of the overcrowded 
plants and may soon 
stop their growth. 
162. Mechanisms 
for distributing seeds. 
Many seeds, such as 
those of the catalpa, 
Bee eke eit the milkweed, and 
eA SA RATT Ae yilon, ite 
The seeds, which are hard and indigestible, are dis- ee eg tufts of 
seminated mainly by birds. One half natural size down which insure 
their being carried 
considerable distances by the wind. Tufted fruits, such as those 
of the thistle and the dandelion (fig. 147), are familiar to most 
people. Sometimes the plant retains the seeds or fruits for 
months after they are ripened, and thus secures their gradual 
dispersal. The globular clusters of fruits of the sycamore 
(fig. 148) remain on the tree during the entire winter—many of 
them even till the new crop of leaves has appeared in the spring. 
Frequently the pod, or capsule, is so constructed that it 
opens at the top (fig. 149) and seatters seeds whenever it is 
swung to and fro by the wind or jostled by a passing animal. 
