28 ECONOMIC BOTANY OF ALABAMA 



rule most abundant in poorer soils ; and they usually grow slowly 

 or are much shorter-lived than trees. It is sometimes convenient to 

 distinguish between large shrubs, taller than a man, like the alder, 

 and small ones waist-high or less. This distinction is not important 

 in Alabama, but it seems to have a real significance in higher 

 latitudes. For example, in northern Michigan, where the ground 

 is covered with two or three feet of snow most of the winter, 

 many of the small shrubs are evergreen, the snow blanket protect- 

 ing their leaves from freezing in zero weather ; while those tall 

 enough to show above the snow are all deciduous. 



A shrub is ordinarily distinguished from an herb by having 

 woody stems which do not die down to the ground in winter; but 

 there are some intermediate and anomalous conditions. For ex- 

 ample, our three palms all have stems which are either under the 

 ground or elevated only a little above it ; but they have large stiff 

 fan-like evergreen leaves, which offer about the same resistance to 

 any one passing through the woods as a shrub of the same height 

 would, and as much concealment for animals, and they are here 

 classed as shrubs. All the cacti have perennial stems above the 

 ground, and some of those in the deserts of the Southwest are 

 large enough to be called trees ; but ours are so low and of such 

 soft texture that they are classed with the herbs. A few creeping 

 plants, like the MitchcUa, have evergreen leaves and perennial 

 stems above the ground, but they are not woody enough to be 

 classed as shrubs. (In colder climates there are many low ever- 

 greens of that nature, sometimes called undershrul)s. j Some of 

 our species of Yucca (all evergreen) have stems several feet tall, 

 while one has its stem almost entirely underground, but they are all 

 called shrubs for the sake of completeness, and also on account of 

 their analogy to the palms. 



Many plants which are only weeds with us, in the tropics 

 where there is no frost to cut them back continue to put out new 

 leaves from more or less woody stems throughout the year, and 

 thus might be called shrubs there. But that class is hardly repre- 

 sented in Alabama, except by the introduced Danhcnton'm, which 

 might be called either a large woody herb or a weak short-lived 

 shrub. 



