Tilden: pilinia and stigeoclonium. 611 



The terminal cell of a sporiferous branch often supported a 

 bristle. PL XXXII, fig. 24, shows a group of three cells termi- 

 nated by a short bristle which it is thought may be a detached 

 branch of this kind. On the other hand it may be a very young 

 plate which has itself thrown off a bristle. The hyaline cells 

 have a diameter of 6 mic. 



The spores in the lower cells of the reproductive portion 

 seem to germinate first. A detached filament composed of 

 nine cells was noticed in which three of the spores had germin- 

 ated. These had developed bristles immediately with no in- 

 tervening cells. 



Mention has already been made of certain cells having under- 

 gone etiolation. This became quite a common condition among 

 the filaments on pebble "3" to such an extent that it was apparent 

 to the naked eye. By the seventeenth day, certain entire thalli 

 had turned perfectly white. No such occurrence was observa- 

 ble in any of the other material. 



Upon the first arrival of the alga it has shown in every case 

 the presence of lime in greater or less quantity. Forming 

 "caps" to the thalli or scattered in microscopic grains through 

 the interior, there is indicated a close relationship between its 

 presence and some physiological function of the plant. From 

 the nature of its structure it appears that its formation takes 

 place after the plant filaments are somewhat matured. 



The green thalli contain a relatively small amount of calcar- 

 eous material while the blue-gray thalli, on the other hand 

 display a large quantity of lime in the form of aggregations 

 or plates of crystals. These plates are in general very irregu- 

 lar in outline. The surfaces are covered with fine ridges 

 arranged horizontally or in concentric lines. PI. XXXII, fig. 20. 

 shows such a crystal- plate. It is seen to be perforated by 

 round holes in the central portion, while at the ends long tubu- 

 lar openings are present. It is not difficult to see that these 

 tubes follow the general trend of the branches in a free branch- 

 ing filament. The fragment here shown has evidently lain in 

 a position at right angles to the direction of growth of fila- 

 ments underneath. As a result the tubes or pipes extend in a 

 direct manner through the middle portion, while at the extrem- 

 ities, as would naturally be the condition from the somewhat 

 radial method of branching which occurs in the upper filaments, 

 the pipes run in an oblique direction. 



A thin fragment of the lime formation lay in a position 

 to show the perforations in cross section. The apertures 



