214 CO-OPERATION OF PLANTS. 



It is necessary to add, however, that lichens as we find them, 

 growing on bark of trees, etc., do not in all cases owe their origi- 

 nal appearance on the locality where found to a fresh union of an 

 alga with a fungus, but there is another mode of distribution of 

 lichens. The distribution of numerous lichens is brought about 

 by the wafting with the wind of already completed social colonies 

 to places often situated a great distance from the locality where 

 the first union of alga and fungus was contracted, the process 

 being as follows : — In a matured lichen, several cells all bound 

 together^ called a soredium, detach themselves from the parent 

 plant, and are blown by the wind to a fresh spot, where, stranding, 

 they establish themselves, commence to grow, and eventually en- 

 large into a full-sized lichen. 



Now, after reviewing the various cases of symbiosis mentioned 

 as occurring between two plants, and also in inquiring into the 

 habits of some animals, we find that we may take a step further 

 and say that many animals and plants have symbiotic relations. I 

 now arrive at the third division of my subject, namely : — Cases of 

 co-operation between certain animals or insects and plants. In 

 such a partnership as this the plant partner is materially assisted, 

 sometimes with food, protection from enemies, etc., by the animal, 

 and in return contributes food, shelter, etc., to the animal. 



Although the two partners may not always live in union 

 (though, no doubt, they do sometimes), yet the reciprocity between 

 them is most perfect, establishing symbiosis conclusively. As the 

 first instance of this kind of co-operation, the well-known action 

 of insects in distributing pollen from flower to flower may be cited, 

 the insect getting as its own share in the transaction the honey 

 from the nectaries of the flowers it visits, while the flowers gain 

 by being cross-fertilised. Then again, many sea anemones have 

 seaweeds growing on them, the anemone receiving material from 

 the weed, and in return contributing matter for the support of the 

 weed. But probably the most interesting example of partnership 

 existing between the animal and plant is that of the fig tree and 

 the wasp. It may not be generally known that in the fig growing 

 countries there are two varieties of fig cultivated. One variety 

 which bears true or edible figs, called the Ficus variety, and 



