10 Dr. G. C. Wallich on the Diatomacea. 



certain well-known laws, which influence the vegetable kingdom 

 generally, exercise an additional and very powerful influence 

 in their diffusion from one bathy metrical zone to another ; and 

 that, too, apart from the peculiar inherent power of locomotion 

 exhibited by this remarkable class of organisms. 



Light and moisture constitute the indispensable requirements 

 of the Diatom. Without these, its vitality at once ceases. But 

 these requirements are essential only in a very modified degree. 

 In other words, an amount of either so limited as to annihilate 

 every trace of life in the higher types, is not only capable of 

 sustaining that of these lowlier ones, but of sufficing for every 

 purpose of luxuriant growth and reproduction. 



It is impossible not to be struck with the exuberant and rich 

 development of endochrome seen in all the floating frustules. 

 Nothing can exceed the vividness of colour or massiveness of 

 the endochrome-granules in the several species observed. The 

 frustules procured direct from the water were invariably full of 

 these particles, whilst such as were obtained, at second hand, 

 from the digestive canals of the minute phyto.phagists within 

 whose bodies they were found, exhibited the frustules in 

 every condition intermediate between that just described and 

 emptiness the exponent of accomplished digestion. In the 

 latter case we have the state in which the silicious skeleton is 

 extruded and now permitted slowly but surely to accomplish its 

 journey to the bottom. 



How far these minute frustules may have travelled from that 

 point at which, succumbing to the limits imposed on their 

 individual existence, or captured as food, they first began 

 their descent as mere motionless atoms, it would be vain to sur- 

 mise. One thing is certain that, to whatever extent their ulti- 

 mate destination may have been influenced by the mightier 

 and more determinate currents of the ocean, they must also have 

 been swayed to and fro, for indefinitely protracted periods, by 

 those numberless fainter heavings which, although unmarked 

 by the plummet, are nevertheless all-powerful in relation to such 

 particles. 



The spores of the freshwater Alga? afford evidence of the 

 wonderful amount of vital resilience, so to speak, with which 

 these structures are endowed, being capable of withstanding 

 long-protracted periods of desiccation under tropical heats, or 

 congelation under Arctic cold, without losing those reproductive 

 energies in the absence of which their tribe would be annihilated. 

 This power belongs in a very marked manner to the sporangia 

 of the Desmidiacea? and Diatomacea?, as is well known. In all 

 probability, therefore, the pelagic Diatomaceai possess some 

 equivalent property, in virtue of which they can the more readily 



