. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . They are, however, only rarely observedunder natural conditions. Under some circumstances, such as when the plants become almost dried 246 Siphonales up, asexual bodies of the nature of cysts or gemnise may be cysts (sometimes rather misleadingly referred to as akinetes)were well described and figured by Stahl (79), after they had been firstnoticed by Klitzing1. They are shortly cylindrical bodies with thick cell-walls, and the
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . They are, however, only rarely observedunder natural conditions. Under some circumstances, such as when the plants become almost dried 246 Siphonales up, asexual bodies of the nature of cysts or gemnise may be cysts (sometimes rather misleadingly referred to as akinetes)were well described and figured by Stahl (79), after they had been firstnoticed by Klitzing1. They are shortly cylindrical bodies with thick cell-walls, and they may either germinate directly into a new filament or theprotoplasmic contents may escape from the old wall before germinationcommences. Very often they break up into amoeboid bodies, which soonround themselves off and become invested with a cell-wall, after which theyeither rest for a time or grow directly into new filaments. In some instances,due as a rule to unfavourable conditions of growth, septa appear at intervals,breaking up the filaments into a number of thick-walled segments which arealso of the nature of rudimentary gemmae or cysts. 00. Fig. 159. The sexual organs of Vaucheria. A and B, V. sesdlis (Vauch.) DC. ; C and D,V. hamata (Vauch.) Lyngb. E, oogoninm and oospore of V. ornithocephala Ag. A—D,x 200 ; -E, x 320. a, antheridiurn ; a?;, antherozoid ; oo, oogonium. Dichotomosiphon produces curious tuber-like swellings at the extremitiesof the branches which may be compared with akinetes (fig. 161 A and Bt).These always grow directly into new plants. Sexual reproduction of a high type occurs in the Vaucheriacese, thisfamily standing alone amongst the Siphonales in the possession of sharplydifferentiated oogonia and antheridia. The sexual organs are developed atscattered intervals along the cylindrical filaments, and, except in the 1 Kiitzing (Tab, PJnjc. iv, t. 98) figured this state of Vaucheria as Gongrosira dichotoma, anunfortunate error which has given r
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