340 THE POPULAR SCIENCE MONTHLY. 



BIOLOGY FOE YOUNG BEGINNEKS. 1 



By SARAH HACKETT STEVENSON. 



T TNDER the low eaves at the back of the house was a long, deep 

 v_J wooden trough for catching the rain that fell on the roof. This 

 old trough was to me a never-failing source of wonder and delight 

 during my childhood. The inside of it was all lined with a beautiful, 

 green, velvety mould, and, when there had been no rain for some time, 

 the water itself would turn a greenish color. We used to catch our 

 little downy yellow ducks and put them in the trough to see them 

 swim, and sometimes they would break off and eat the green mould 

 with their curious shovel-bills. What this queer, green stuff was, and 

 how it came there, was a great mystery to us children. Charley de- 

 clared it came down in the rain just as the angle-worms that he used 

 for fish-bait. I had to wait a long time to find some one to explain to 

 me all about these simple things. No doubt I might have learned 

 about them here at home, if I had tried hard enough ; but it so hap- 

 pened that I found a great professor in London, who was teaching his 

 students just what I wanted to know, and he explained so well what I 

 had seen in the old water-trough, and many other curious things, that 

 I have thought my young friends might like to hear about them also. 

 I am sure I should have been very glad if I could have found any one 

 to explain them to me when I was a child. 



Probably you have no trough in which you can find this green 

 mould, but there is plenty of it on old palings, stone-walls, and the 

 trunks of trees. That which comes on the top of water, and makes it 

 look green, is a little different from that which covers old wood and 

 stones, and we shall speak of this difference by-and-by. In order to 

 see what there is in this green, mouldy matter, and what it is made of, 

 you must look at it through the microscope. The word microscope 

 comes from two words which mean little, and to view, and so this in- 

 strument is used to magnify, or make larger, things which are too 

 small to be seen with the naked eye. Under it the dust of the butter- 

 fly's wing looks as large as the feathers of a canary-bird. Each of you 

 ought to have a microscope of your own to study the things we are 

 going to talk about, or several of you might club together and buy 

 one, and use it " turn about." I am sure you would never regret the 

 investment. 



If you carefully scrape off a little of this mould from the trees or 

 fences and look at it through the microscope, you can see that it is made 

 up of exceedingly small bladders or bags. You will find little sacs 



1 From " Boys and Girls in Biology," now in the press of D. Appleton & Co., by a 

 pupil of Prof. Huxley. Written upon the basis of his lectures, and illustrated by Miss 

 M. A. J. Maeomish. 



