12 THE DIATOMACEvE OF PHILADELPHIA AND VICINITY 



THE MOTION OF DIATOMS 



The erratic backward and forward movement of certain diatoms, especially those of 

 the Naviculoid group, or the slow, rolling motion of Surirella, has been discussed in so many 

 ways without definite conclusions that a brief statement will be sufficient. Osmosis, the 

 amceboid movement of the coleoderm, the protrusion of protoplasm or protoplasmic threads 

 through the raphe, the existence of actual organs of locomotion or cilia, and the lack of 

 synchronism in the chemical action occurring at the ends of the cell which is sometimes 

 divided by the plasma bridge, have been offered in explanation. The chief objection to the 

 theory of cyclosis appears to be that the resultant motion is so greatly in excess of the rota- 

 tion of protoplasm in the cell. More or less motion is observed in various kinds of free cells, 

 but the movement of diatoms is not evident in those without either a raphe or a keel upon 

 which and apparently by which the phenomena are produced. 



Mr. T. Chalkley Palmer, in various articles in the Proceedings of the Delaware County 

 Institute of Science, especially in Vols. 1 and 3, gives the results of exhaustive experiments. 

 "Nothing, it would seem," he says, " could be more conclusive as to the essential sameness 

 of the nature of motion in monads and diatoms, than the fact that both monads and diatoms 

 require oxygen in order to perform motion, that they come to rest when oxygen becomes 

 scarce, and that they resume their motion when oxygen is again supplied." 



He also thinks "that the living substance of the cell, more or less deeply overlaid with 

 coleoderm substance of varying consistency, and itself assuming that degree of fluidity 

 which best meets the requirements of the situation, permeates the raphes, circulates in the 

 keels, or in some cases protrudes quite beyond the silica, and functions as the actual pro- 

 pulsive agent." 



THE FUNCTION OF DIATOMS 



Of all forms of vegetation, the Diatomaceae are, perhaps, the most ubiquitous. Where- 

 ever a sufficient amount of moisture, heat and light are found, they grow. It was during 

 the Miocene period that they first appeared, and, as marine forms, reached their greatest 

 development, both as to size and beauty of marking, while their prevalence throughout the 

 world in enormous quantities has been often mentioned. The Miocene beds of Richmond 

 and Maryland continued over the Cretaceous formations of New Jersey have outcropped 

 in certain localities within our district, but are not considered in this discussion. 



The function of diatoms is not essentially different from that of other algse in provid- 

 ing food for aquatic animals, such as Salpae and oysters, but it is, however, in other respects 

 that they are not only important but necessary factors in the preservation of life. 



"Full nature swarms with life; one wondrous mass 

 Of animals, or atoms organized, 

 Waiting the vital breath, when parent heaven 

 Shall bid his spirit blow. The hoary fen, 

 In putrid streams, emits the living cloud 

 Of pestilence. Thro' subterranean cells 

 Where searching sunbeams scarce can find a way, 

 Earth animated heaves." 



I am not certain if Thomson fully understood the matter, but he has remarkably 

 described the facts. When "the vital breath" of returning spring animates the earth, the 

 "subterranean cells" of diatoms, the "atoms organized," through the liberation of vast 

 quantities of oxygen, immediately begin the purification of the "putrid streams." Were 

 these streams not so purified, the accumulation of animal and vegetable debris would event- 

 ually cause an enormous bacterial growth fatal to animal life. 



