CHAPTER XXV. 



BACTERIA, ALG.E, FUNGI, AND LICHENS. 



AMONG living things two processes must be maintained; first, 

 the nutritive, on which the life and vigor of the individual plant 

 or animal depends; second, the reproductive, on which the life of 

 the race, the perpetuation of the species, depends. The differences 

 in structure among plants, and the modifications of structure by 

 which the plant adapts itself to its surroundings, are important 

 items to consider in the study of plants. The structure of plants 

 and the processes of nutrition and reproduction comprise nearly 

 all the work of botany. 



There are a great many kinds of plants, and it would be an 

 endless task to try and study each one ; but many plants are 

 similar to other plants in structure, in methods of reproduction, 

 etc., so that a careful study of one plant gives a good idea of 

 many similar plants. Plants are divided into species, genera , 

 families, orders, divisions, etc. On the basis of structure we have 

 cellular plants, made up wholly of parenchyma, and vascular 

 plants in which the vascular bundles are prominent features of 

 the structure. These groups are separated into divisions mainly 

 on the basis of differences in the reproductive processes. 



The division including the lowest plants is called PROTOPHYTA, 

 first plants. These are the lowest and simplest plants, usually of 

 minute size; the cells are poorly developed, and often there is no 

 cell wall. In many cases the plants consist of only one cell, and 

 when there is an aggregation of cells, the union is usually so 

 slight that each cell is practically an individual. 



If we add a few drops of yeast to a solution of sugar and keep 



it in a warm place, the mixture will soon become turbid and then 



frothy, will lose its sweetness and acquire a spirituous odor, and 



at length a scum of yeast will collect on the surface of the liquid. 



(190) 



