LUTHER BURBANK 
only those vegetables of the simplest type which 
reproduce by splitting themselves in two. In 
this subkingdom live the death-dealing bacteria, 
which bring about such human diseases as tuber- 
culosis and malaria, or such plant diseases as 
black rot; and the good bacteria, too, which are 
everywhere, helping us to digest our food, and 
without whose help the higher subkingdoms of 
plant life could not exist; and other plants of the 
same grade. 
The next subkingdom, higher by a step, includes 
the yeast which we use to raise our bread, or those 
microscopic vegetables which turn hop juice into 
beer, apple juice into cider and rye juice into 
whisky; and others. Those who prefer to chart 
seven subkingdoms instead of six, divide this 
branch into two, making the slime-molds a 
separate phylum. 
The next subkingdom, ascending the scale, 
includes, among others, the mosses and liverworts. 
From these it is but a step to the next sub- 
kingdom, which includes the ferns—the highest 
type of flowerless plants, and the first, in the 
ascending scale, to exhibit a complete development 
of root, stem and leaf. 
The final subkingdom, and the one into which 
our work principally takes us, embraces those 
plants which produce seeds. 
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