202 The Microscope. 



Prof. J. D. Cox read a paper on 



" SOME DIATOM HOOPS AND THE QUESTION OF THEIR MODE OF GROWTH." 



Mr. Cox explained for the benefit of those unfamiliar with 

 diatoms, that they are botanically known as "unicellular algae,'' 

 which secrete silexin the covering membrane, until they be- 

 come glass boxes of minute proportions, filled with the live con- 

 tents common to vegetable structures. But this inflexible box 

 makes the matter of growth a problem having its own difficulty. 

 The diatom follows the mode known as fissural division, in which 

 the shell contents divides into two, forming two new cells which 

 grow to the size of the parent. This again implies the enlarge- 

 ment of the whole mass to double the former size, and the 

 newly demanded space is furnished by the sliding of the valves 

 upon each other teloscopically. The sliding parts are called the 

 hoops. This introduction leads to the points aimed at in the 

 paper. A beautiful diatom was described, a disc form orna- 

 mented by a peculiar cross shaped arrangement of dots or cel- 

 lules. Between the two valves which form the box the hoops 

 intervene. In this species these hoops are clear and transpar- 

 ent, but are in rings separated by sutures, at which they readily 

 separate when ripe. These sutures are so shaped that in each 

 ring is a tooth pointing toward the valve to which the ring is at- 

 tached. When separated at the sutures each ring is a band with 

 a boldly-projecting tooth on one side, but interrupted at the ex- 

 tremities, so that it is not a complete ring, but a bent band, with 

 the ends approaching each other. The paper then took up the 

 question of the mode of the growth of these rings, saying that 

 the prevalent theory has been that they grew at the edges. Mr. 

 Cox, however, maintained that these sliding hoops do not grow 

 at the free edge, but that they are formed as a membrane 

 directly from the live contents of the single cell, and upon its 

 surface. This view was supported by various arguments. 



After the usual vote of thanks, and after a few well chosen 

 words from the new President-elect, the society adjourned sine 



die. 



The above brief report conveys but a slight idea of the char- 

 acter of the papers presented, or of the enthusiasm awakened. 



Over fifty new members were elected, and there were 

 nearly 200 members in attendance. 



