USEFUL AND HARMFUL PLANTS 303 
tain animals may be fatal to themselves. Since, however, 
some of these plant poisons are among the most valuable of 
medicines, it is plain that no dividing line exists between 
harmful and useful plants. - Judged in its relation to our 
welfare the same plant may be either useful or harmful 
according to what we do with it. Obviously, the more we 
know about their properties the less likely are we to suffer 
harm from plants, and the more likely are we to benefit by 
them. 
The student should understand clearly that in this book the 
aim is only to introduce beginners to the study of plants. 
Our purpose is merely to lay a good foundation for future 
studies which shall further advance general culture. There 
has been no intention of giving here a complete outline of — 
economic botany. Accordingly, a great many plants of high 
economic importance have not been mentioned; and some 
of the chief uses of plants, and some of the most serious ways 
of their working harm, have been passed over with bare 
mention, or have been ignored. Thus, in regard to the food 
of domestic animals but little has been said of the fod- 
der raised for them, and nothing at all of pasture plants 
upon which some of the principal industries of the world 
depend. The many plants which afford bees the material 
for making honey and wax, and those which serve as food for 
silkworms or other insects of economic value have also been 
neglected. So also have we omitted reference to the plants 
which do great service in binding shifting sands that but 
for these sand-binders would devastate extensive areas: to 
those plants similarly used to prevent the washing away of 
soils; to trees set out as wind-breaks for protecting tender 
vegetation, as drainers of swamp land, or for shade and 
beauty; and to the innumerable flowers and foliage plants 
cultivated or collected for ornament. Likewise, among 
harmful plants neither. weeds nor destructive parasites have 
been included. 
Not only has our study gale ee these groups of plants 
which especially affect the welfare of mankind but it has 
been forced to leave out of account some most extensive in- 
fluences which vitally concern animals in general. For ex- 
