404 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



WHAT ARE ALGAE? 



The word "alga" (singular), "algae" (plural) comes from the 

 Latin and is used by us to designate the large class of plants, the 

 algae, which are the lowest and simplest in organization of all the 

 plants in the plant kingdom. The algae, like all the plants with 

 which we are familiar, possess chlorophyll, or green pigment, and 

 are thus able to make their own food from inorganic materials such 

 as carbon dioxide, water, and certain mineral substances with the 

 aid of light. Alga is derived from the Latin word "algor" which 

 means "cold." 



The algae include the seaweeds and unicellular and multicellular 

 green plants that do not possess a true stem, a true root, true leaves, 

 or true seeds as are found in the higher plants. All of the life proc- 

 esses of the algae — respiration, photosynthesis (the manufacture of 

 their food), and reproduction — are organized within their cells. Al- 

 though they do not have true organs — root, stem, leaves, and seeds — 

 they possess the green pigment called chlorophyll which is charac- 

 teristic of plants and essential for the production of their food. 



The lower algae include plants whose whole framework consists 

 of an individual, isolated cell such as the Diatomaceae, Desmidiaceae, 

 and Palmellaceae. Every function of life is performed within the 

 cell: the assimilation of gases and salts, the manufacture of their 

 own food, and growth until the cell reaches the size proper to its 

 species. Then the nucleus within the cell gradually separates into 

 two portions and at the same time a cell wall is formed between 

 each portion, thus forming two cells from the original one cell. 

 These two cells do not adhere to each other as cells do in a compound 

 plant, but each half-cell separates from its fellow and starts out 

 on its own independent career: food manufacture, increase in size, 

 division at maturity, and then separation of the contents occurs 

 again. In spite of the fact that these infinitesimal plants are micro- 

 scopic in size with their uniform and simple structure, they have 

 an innumerable variety of exquisite and artistic forms, and the secrets 

 of their mechanism are still puzzling and intriguing the scientists. 



In other low forms of algae, the cell is cylindrical and sometimes 

 lengthened into a threadlike body, or the lengthened cells are joined 

 end to end as in the Oscillatoriaceae. There is a further advance in 

 the Vaucheriaceae, where the filiform cell becomes branched without 

 any interruption to the plant body; and these branching cells some- 

 times attain inches in length with the diameter of half a hair and 

 constitute some of the longest cells among plants. In the nearest 

 genera to Protococcus the frond is a roundish mass of cells which 

 cohere irregularly by their sides ; then more advanced are the Ulvaceae 

 where the cells are arranged in a compact membranous expansion 



