September, 1928 



EVOLUTION 



Pace Eleven 



The Amateur Scientist 



A Monthly Featuke conducted by Allan Strong Broms 



AMOEBA, THE ONE-CELLED 



THE FALLING LEAVES 



Amoeba, one of the simplest of all The leaves are turning to autumn tints 



animals, consists of a single, shapeless and falling. That is the plant's way of 

 cell and is therefore microscopic in size. saving the green stuff which gives it life. 

 It should be looked for in tlie slimy coat- This green stuff, called chlorophyll, when 



exposed to sunlight 

 Eiid..pi.isni EciopLism storcs away the energy 



i)f the light in the food 

 materials which it builds 

 up out of such sub- 

 stances as water, gases 

 and soil material. 



Pseiijopodi 



Psciidopod^ 

 rctrLitting 



Contractile vacuole 



Food vacuoles 



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Amoeba; its structure, changes 

 production by division. 



shape, 



ings of leaves or stems submerged in 

 stagnant water or on the slimy ooze of 

 the^ bottom mud. Of course, a drop must 

 be placed on the microscope slide and a 

 cover glass placed gently over it. Then 

 comes the real job of finding it, for its 

 slowness of movement and lack of defin- 

 ite shape make it easy to miss. It is just a 

 speck of clear, colorless jelly with a deli- 

 cate, yet distinct outline. Within it appears 

 a denser nucleus and occasionally a clear 

 space, the contractile vacuole. 



If the object under suspicion is really 

 an amoeba, it will presently betray itself 

 by moving. One side will bulge into a 

 projection called a pseudopod (false foot) 

 or perhaps several of them. The pseudopod 

 may be retracted, but often the rest of 

 the body flows into it, resulting in loco- 

 motion, often in a consistent direction. 



If a food particle happens in the way, 

 a pseudopod extends to engulf it, usually 

 with a little water. The space thus occu- 

 pied is called a food vacuole and slow- 

 ly disappears as the food is digested and 

 absorbed. Waste matter is merely left be- 

 hind as the amoeba flows away. The whole 

 or any part of the body acts as stomach, 

 while the surface in all its parts serves as 

 mouth, lungs or excretory organ as occa- 

 sion demands. It also seems to have a sense 

 of touch, for it often avoids obstacles in 

 its way, though this may be simply a 

 chemical reaction of its jelly stuff. 



When well fed, the amoeba may repro- 

 duce by simply dividing into two. Its 

 middle becomes constricted, the nucleus 

 divides and the constriction increases un- 

 til the two halves part, each a complete 

 amoeba. On the other hand, when sub- 

 jected to drought or other unfavorable con- 



Water vacuoles -p^e cold of winter 



will stop the flow of the 

 plant sap which carries 



> .'^ i the supply of materials 



f .," : and the food to and 



:; , . from the leaves. It is 



- ' therefore an economy to 



withdraw the valuable 

 ':o-.' ■ ■; chlorophyll from the ex- 

 ■ * ^ posed leaves before the 



frost begins to bite and 

 kill. So it is withdrawn 

 ' o , well into the body of the 



.,'■.■■' .■ tree. The leaves thus 

 lose their green and the 

 and method of re- reds and yellows now 

 appear to glorify our 

 landscapes. 

 When the withdrawal is completed, a 

 thin layer of cork appears between the 

 base of the leaf stem and the woody 

 branch. This seals the wound that would 

 otherwise be left when the leaf falls. Next 

 spring, when the sap begins to flow once 

 more, the new leaves bud out, green witli 

 the life-giving chlorophyll that has been 

 saved, to do their work of food manufac- 

 ture. Trees that use this method of shed- 

 ding their leaves each year are called de- 

 ciduous. 



The evergreen trees have found a differ- 

 ent solution by forming fat, needle shaped 

 leaves which do not freeze so easily be- 

 cause they have less surface exposed. 

 These do not fall off seasonally, but do 

 their work on every day that is warm en- 

 ough. As they usually live in a cold 

 climate or at high elevations where spring 

 comes late and winter early, each day of 

 warmth and sunshine must be used, with 

 no time for getting ready by growing new 

 leaves. • 



Each method has been evolved by the 

 survival of those plants that varied to fit 

 these differing conditions of their sur- 

 roundings. Those that did not fit. died 

 out, while those that did fit, lived on and 

 spread their kind. 



ditions, it forms a tough outer wall or 

 cyst and remains dormant. When favorable 

 conditions return, it ruptures the cyst, 

 crawls out and renews its sluggish life. Our 

 first ancestors must have resembled amoeba. 



FOPL'LAR ASTRONOMY LECTURES 



New York City readers should attend 

 the popular lectures given by the Ama- 

 teur Astronomers Association at the Ameri- 

 can Museum of Natural History at 8:15 

 P. M. oil the first and third Wednesdays 

 of each month. The next, October 17th, 

 is by Dr. H. T. Stetson of the Howard 

 College Observatory on the subject, "What 

 of Sun Spots." 



CIRCULATION OF THE BLOOD 



The circulation of the blood can be 

 seen in the thin web of a frog's foot. 

 One with a pale web is best. The frog 

 should be wrapped in a wet cloth, with 

 one leg projecting, and then tied to a 

 piece of shingle. Cut a hole in the shingle 

 under the frog's foot. Tie threads around 

 two of the toes and stretch the web, not 

 too tightly, over the hole. 



Now put the stretched web under a 

 low power of the microscope. The large 

 lubes are arteries which subdivide into a 

 network of fine capillaries which then join 

 into veins. The capillaries receive the 

 blood from the arteries and pass it on 

 to the veins. The pulsing streams of blood 

 can be clearly seen, particularly in the 

 arteries. 



Under a high power, the large oval and 

 slightly colored corpuscles are individu- 

 ally visible as they rush past. They are 

 the boats of the blood stream carrying 

 lood matter and oxygen to the body tis- 

 sues and carrying away the wastes. There 

 are also other corpuscles, smaller, round- 

 er and paler, fewer in numbers and mov- 

 ing slowly and unsteadily along the sides 

 of the tubes, the so-called white corpu- 

 scles. One of their important jobs is to 

 protect the body against diseas.e mic- 

 lobes. 



To examine the corpuscles more clear- 

 ly, they must be stopped. The easiest way 

 is to place a drop of the frog's blood on a 

 microscope slide, with a thin cover glass 

 over it, and examine it with a very 

 high power. You can do the same thing 

 with a drop of your own blood. The com- 

 parison is very interesting. When you have 

 had a good look, unwrap the frog and let 

 him go. He has contributed his share; 

 give him a chance. 



"Faith." said the little boy, "is the 

 power of believin' things you know aint 

 so." 



l-'ino IiUmhI vessels in frog's foot, showing; 

 ulilrin.LT-red and round-white corpuscles. 

 .\rrows show direction of blood tlow. 



