342 THE POPULAR SCIENCE MONTHLY. 



green leaf. It is easy to remember ; it will belp you to think of the 

 hard Greek name chlorophyll. 



The little round, hard kernel is called the nucleus, which means a 

 nut or kernel, and the thin space in the centre is the vacuole or air- 

 cell. It seems to be like a tiny drop of water separated from the rest 

 of the jelly, which contains a good deal of water. 



Now that we have described and named each of these different 

 parts, we can go a step or even two steps farther, and tell of what the 

 most of them are made, and of what use they are. The tough wall or 

 sac of the cell is made of the woody matter or cellulose, mixed with a 

 little water and mineral matter. The cellulose or woody part is made 

 of three substances carbon, hydrogen, and oxygen. If you ask me 

 what these things are, I can only tell you that they belong to what are 

 called the simple chemical elements, because each one is made of just 

 one kind of matter. These three substances, and one other called nitro- 

 gen, help to make every thing there is in the world, except a few such 

 things as gold, iron, sulphur, etc., which are also simple elements. The 

 water is made of hydrogen and oxygen. Its use is probably to hold 

 and protect all the inside parts, or contents of the cell. So much for 

 the outside sac of the cell now for the inside. The cell-jelly, or proto- 

 plasm, is made of water, fat, mineral matters, and protein. The water 

 we already know. The fat is made of carbon, hydrogen, and oxygen. 

 The minerals belong to the simple elements. 



The protein we know but little about. We are sure that it con- 

 tains carbon, hydrogen, oxygen, and nitrogen, with a little sulphur or 

 phosphorus, or both, and we know that it is found in all living matter. 

 There is no life without it, so it has been called the " basis of life." 

 But there is a great deal more to be learned about it. I want you 

 to remember what this word protein stands for, because it is some- 

 thing about this substance that makes one of the greatest differences 

 between vegetables and animals. There is nothing in its appearance 

 that would make you think it of so much importance ; it looks to be 

 nothing more than" so much light-colored jelly, or white of egg. The 

 word protein means first or chief, and this is the part of the proto- 

 plasm-jelly, which is alive. The kernel, or nucleus of the cell, seems 

 to be only a part of the protein-jelly which is harder than the rest, 

 and it has something to do with the making of new cells, as we shall 

 see farther along in our study. 



Now, what about the dye-stuff? Is it of any use, or is it just here 

 to make the mould look pretty ? It is of great use, as we shall soon see. 

 Each grain is a very clever little chemist that works in the cell, which 

 is his laboratory, or workshop. The sunlight is the fire by which 

 this chemist heats his crucible, or melting-pot. Into this crucible he 

 puts the poisonous gas, carbonic acid, that he gets from the air, and 

 melts it up into carbon and oxygen, the two substances of which it is 

 made. He keeps the carbon to feed upon, and gives back the pure 



