374 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 2 



Although we all dislike algae in our drinking water, they are of 

 use to modern science. For algae, the tiny celled organisms that 

 make up green pond scum, contain in each little cell some of the 

 green pigment called chlorophyll. It is this pigment that is most 

 essential to both the plant and the animal world. Not only the 

 food which plants themselves use but the food of man and all other 

 animals comes from plants. The manufacture of this food is made 

 possible by the chlorophyll in the presence of light. 



This green pigment is present in higher plants, for example in 

 the leaves of the oak tree and lettuce, just as it is found in the algae 

 which are lower plants. A small amount of it is contained in each 

 little cell, millions of which constitute a leaf. All cells divide and 

 redivide many times. In the leaf the cells remain united to in- 

 crease the size of the leaf as a whole, but in the unicellular algae 

 the cells are separate. Many algal cells are so tiny that one single 

 cell filled with green chlorophyll can be distinguished only under 

 a microscope. 



Scientists in their search to discover the effect of light, tempera- 

 ture, humidity, nutrition, and poisons on plants and chlorophyll find 

 that often a higher plant composed of millions of united cells pre- 

 sents complications that hinder research. Since physicists and 

 biologists have cooperated to study the mechanism of the plant cell, 

 very intricate and delicate pieces of apparatus have been devised. 

 Cells combined in tissue do not always give a correct indication of the 

 processes that take place in the growing plant, for no matter how 

 carefully the tissue is removed from the plant, the cells are harmed 

 and will not long continue to live. But a single-celled alga carries 

 on all the life processes in its one cell, so that it can be moved from 

 its normal habitat and placed in conditions for experimentation with 

 the assurance that it is registering its reaction to them. The single 

 cell has two other advantages. The less complicated the organism, 

 the less individuality it presents ; also, the smaller the organism, the 

 greater the number of organisms on which observations can be based. 

 Both these factors tend to reduce uncertainties due to individual 

 differences. 



When a drop of water from a pond green with slime is examined 

 under the microscope it is astonishing to see that the drop is a tiny 

 world in itself. For not only are bright green cells of algae present, 

 but also star-shaped and moon-shaped diatoms, bright yellow and 

 orange yeast cells, infinitesimally small bacteria moving so fast that 

 the eye can scarcely perceive their shape, long blue-green ribbons 

 of multicellular algae, and a tangle of fungous cells. There are ani- 

 mals, too — transparent paramoecia turning and twisting, and jelly- 

 like amoebae flowing about, all trying to engulf the plant cells. The 



