CHAPTER I 



filaments. The term spore is applied to a protoplast that is capable of 

 growing into a new plant, and the prefix " zoo " means behaving like 

 an animal, that is, moving. The pond-scums do not produce zoos- 

 pores but form strong resting spores by a union of the contents of 

 two cells, as shown in Fig. 4, Nos. I and 4. These conjugating fila- 

 ments are frequently found in nearly exhausted pools ; without the 

 microscope they look rather broken up and spoiled. 



Among the plants brought by children to illustrate this lesson there 

 may be a dark blue-green slime that they may have found coating the 

 sides of ditches or reservoirs. This is likely to be Oscillatoria, and it 

 belongs to the lowest group of plants, the Protophytes, the group that 

 includes bacteria. A minute bit of this slime, undisturbed in a dish 

 of water, will show radiation of the filaments in less than an hour, 

 and in twenty-four hours it will exhibit in a striking way the move- 

 ments of the plants in order to secure better conditions for food. To be 

 sure, this movement may be mistaken for growth. The children will 

 be quite likely so say that the plants have "sprouted" or floated. 

 The microscope will demonstrate the movement, which is mainly an 

 oscillating one. But in default of the microscope, children will take 

 the fact of movement on authority and will be interested in watching 

 evidence of it and in thinking out its use to the plants. They will be 

 quick to discover the slime on damp walls and flower-pots, and green 

 film on stagnant pools ; and they will gradually become impressed 

 with the fact of the existence of a wonderful microscopic world. 

 This world appeals to children's imaginations, and while most uni- 

 cellular plants, especially bacteria, are much too small to be handled in 

 elementary work, a well informed teacher will find no difficulty in 

 impressing children with some practical truths about them. 



If microscopes are used at all, some unicellular organisms are 

 pretty sure to be encountered incidentally in work with fresh water 

 Algae ; the pretty, green, crescent-shaped destnids, perhaps; or little 

 active, transparent infusorians ; or, most common of all, little, 

 brown, boat-shaped organisms, diatoms, that move about in a jerky 

 way. The desmids are plants, the infusorians animals; the diatoms 

 are still included among plants in most text books in Botany, but 

 excellent authorities have of late relegated them to the animal king- 

 dom ; so thus the fact that there is no sharp dividing line between the 

 plant and the animal world is illustrated. 



Children who live by the sea, or even those who visit the sea only 

 occasionally, should not miss the pleasure of becoming acquainted 

 with some common marine Algae. The teacher can, in one visit to 

 the sea, lay in a stock of specimens that will last for years. The 



