68 DIATOMS. 



while in my office related an experience of his in pho- 

 tographing plants last summer. In order to preserve the 

 true color values of leaves and flowers he used the ortho- 

 chromatic plates with a yellow screen, consequently em- 

 ploying a very long exposure in order to get sufficient 

 detail into his negatives, when he ran against a most un- 

 expected obstacle. He couldn't get his plants to keep 

 still long enough to have their pictures taken. The 

 leaves and stems of flowers writhed and twisted to such 

 an extent that he considered himself fortunate if he ob- 

 tained one good negative for three or four plates. Each 

 diatom consists of a single cell which forms — no matter 

 what its shape may be — a little box. If we take a pill 

 box for an illustration the top and bottom of the box 

 represent the two valves of the diatom and the sides of 

 the box and of the cover the two connecting bands or 

 zones which slide over each other. The valves and often 

 the zones are covered with ornamental markings often of 

 the most elaborate character, and these markings add 

 greatly to the beauty of the specimens. 



Inside this small box we find at the centre a little mass 

 of protoplasm which is called the nucleus and in this 

 nucleus is a minute dot called the nucleolus. Arranged 

 in various patterns according to the genus of the plant 

 are masses of yellowish material called the endocTirome. 

 This is the same substance substantially as the chloro- 

 phyll or green coloring matter of the higher plants, and 

 performs the same function, i. e. of splitting up the car- 

 bonic acid in the water into carbon and oxygen and set- 

 ting the latter free. In a single specimen the color is a 

 tawny yellow, but when seen in large masses it is a pe- 

 culiar shade of brown. 



By setting free the oxygen this substance purifies the 

 water for animal life. Sandwiched in with the endo- 

 chrome is a mass of protoplasm somewhat less dense 

 than the nucleus, and interspersed throughout the cell 



6 



