Protoplasmic continuity 15 



been observed in the heterocysts and in the germinating spores of Gloeotrichia 

 and Anabtena. 



(6) Pseudovacuoles. Certain of the free-floating Myxophyceae, more 

 especially of the genera Gloeotrichia, Anab&na, Aphanizomenon, Ccelo- 

 sphferium, Microcystis, etc., which sometimes occur abundantly in the 

 plankton, contain 'granules' of a more or less dark red colour scattered 

 through the cytoplasm. These granules were originally discovered in 

 Gloeotrichia echinulata by P. Richter ('95), who at first described them 

 as granules of amorphous sulphur, but afterwards regarded them as an 

 optical illusion due to an alveolated protoplast. The red appearance, which 

 is not very pronounced, is probably caused by diffraction. Klebahn ('95) 

 and others have concluded that they are gas vacuoles, directly concerned 

 with the floating capacity of the Alga? which possess them. They often 

 appear almost black, and are removed by treatment with absolute alcohol 

 or chromic acid. Klebahn, experimenting with Glceotrichia, and Molisch ('03) 

 with Aphanizomenon, both state that the granules are not removed on placing 

 the water containing the Algse in a vacuum. Molisch, therefore, rightly 

 concluded that they cannot be gas vacuoles, but expressed the opinion 

 that they had a specific gravity less than that of water, and he termed them 

 suspensory bodies. Lemmermann ('07), on the other hand, points out that 

 those Blue-green Algas containing ' pseudovacuoles ' can be caused to sink by 

 keeping them for a long time in a mixture of alcohol and glycerin, or in 

 2 4 per cent, formalin, without losing these bodies ; and further, that some 

 blue-green forms which are always fixed to a substratum also possess 

 ' pseudovacuoles.' Fischer attributes these bodies to the optical effect of 

 his so-called ' pseudomitosis of anabsenin ' ; but if so, all Blue-green Algse 

 should possess ' pseudovacuoles,' which is not the case. 



It is obvious from the foregoing remarks that our information concerning 

 ' pseudovacuoles ' is altogether insufficient, and that statements as to their 

 nature are as yet largely conjectural. They are chiefly found in the 

 Myxophyceas of the plankton, organisms which are exposed to relatively 

 intense light. They also appear in the hormogones of Nostoc, Phormidium, 

 and Lyngbya, especially in those parts of the stratum exposed to the 

 brightest light. In view of the fact that most Myxophyceas without 

 ' pseudovacuoles ' live to a great extent in feeble light, either as shade plants 

 or by reason of their strongly coloured sheaths and integuments, Lemmer- 

 mann has suggested that the ' pseudovacuoles ' are possibly protective bodies 

 against light of too great intensity. 



PROTOPLASMIC CONTINUITY. In some of the filamentous Myxophycea3 

 there exists a protoplasmic continuity between the cells. Wille ('84) was 

 the first to point this out in Stigonema compaction var. brasiliense. Borzi ('86) 



