PTTUE CROP OF UNIFORM AGE. 15 



loped, succulent twigs and foliage or roots; but weak plants, grow- 

 ing in the midst of, or closely surrounded by, stronger individuals, 

 are often left untouched. The goat will often overlook small plants 

 and stand up to one bearing leaves as high as it can reach. Be- 

 sides the injuries already described, herbivorous quadrupeds may 

 hurl: or kill plants also by trampling them down, or by treading tho 

 soil into a hard pan, or by digging up or loosening with their feet 

 the soil round them and thus injuring or, as often happens on steep 

 ground, completely exposing their roots. Birds may peck off 

 leaves, buds and young shoots, besides breaking them by perching 

 on them* And so on. Hence it is not invariably, nor generally, 

 the weaker plants that succumb to the attacks of animals, 



(ft) Attacks of parasitic and epiphytic plants. Some parasitic 

 plants will, as a rule, attack only unhealthy individuals. Certain 

 fungi, if they can only obtain a lodgement in some unhealthy or 

 diseased part, will overrun an entire tree, however healthy it 

 might otherwise be. Other fungi again, especially those that 

 spread by way of the soil or enter through the stomata, will di- 

 rectly attack the most healthy trees. Purely epiphyllous fungi, and 

 those caulicolous species which do not overrun an entire tree but 

 cause only local injuries, will obviously influence the mutual struggle 

 for existence more than tlm-e species which spread through every 

 portion of the tree attacked and are thereby able at once to invade its 

 immediate neighbours and thus rapidly involve them in the same 

 doom. Woody parasites, like the mistletoe family, frequent weak and 

 strong plants indifferently. The damage they do is usually con- 

 fined to starving and killing the portion of the branch above the 

 point at- which they have fixed themselves. Some parasites, like 

 the Ci(*:'i/t t, overspread the entire crown of their host, sucking out 

 the elaborated sap through their countless haustoria, and in this 

 manner not only rob it of its nourishment but also suppress a more 

 or less considerable part of its foliage. 



Epiphytic plants make no distinction between weak and strong. 

 The sinu'ler epiphytes can, of coui-se, do no damage, while the 

 larger ones, like the figs, hurt their temporary hosts by over- 

 topping them and thus suppressing their crowns and encks'ng 

 their steins within their nume.rous coalescing aerial roots. 



(>) Injurious climatic influences frost, drouyht, sunstroke, hail, 

 ruin, iriud, snow, l><j!itnirj. eye. Other conditions being the same, 

 all plants will suffer equally from these causes, especially from frost, 

 drought and hail. But as some plants will necessarily be taller or 

 stronger or better lignified or more deep-rooted or in any other- 



