28 



Myxophycese 



They are sometimes solitary, but more often seriate, and the longest chains 

 of spores are those found in Nodularia, Scytonema and Hapalosiphon. In 

 some species the spores are enveloped in an external gelatinous investment, 

 which may be very thin, as in certain species of Nostoc, or thick and firm, as 

 in some of the plankton-species of Anabxna. In Anab&na Lemmermanni 

 the spores agglutinate in masses, which float in such quantity in the surface 

 layers of water as often to give a deep colouration to a whole lake. 



Before germination the spores undergo a more or less prolonged rest, 



which in Hapalosiphon, Scytonema, and 

 the plankton-species of Anabwna ex- 

 tends over many months 1 . 



The germination of the Testing- 

 spores has been followed out in a 

 number of different forms and, although 

 there is some variation in the actual 

 mode of germination, in all cases it 

 results in the more or less direct for- 

 mation of the typical vegetative plant. 

 This first-formed filament may in some 

 cases break up into hormogones, each 

 of which grows into a new plant. 

 There are three main types of germi- 

 nation of the spores : 



(1) The protoplast contracts from 



the wall of the spore and escapes either through a pore in the wall or by 

 a lid-like portion of the wall becoming detached and so providing an orifice. 

 The escape of the contents is a very gradual one and is primarily brought 

 about by the secretion of mucilage, which forces the protoplast through 



B 



Fig. 17. A, resting- spores of Hapalosiphon 

 Welwitschii W. & G. S. West, x 520; 

 B, spores of H. luteolus W. & G. S. 

 West, x 520 ; C, spores of Scytonema 

 coactilc Montagne, x 500. 



1 Fritsch ('04) found that in Anabaena azollse the spores can germinate as soon as they are 

 fully formed, but this observation was made on material in cultures. It must also be borne in 

 mind that A. azollse, is one of the greatly specialized forms of Myxophycere, and observations on 

 this or any other equally aberrant species do not affect generalizations based upon normal 

 members of the genus, or upon species of other genera. It is interesting to note in this connec- 

 tion that in another similar specialized species of Anabsena (A. cycadearum) the spores in 

 culture-material are capable of immediate germination. The author has also found that spores 

 of Nodularia turicensis which had been developed in cultures were able to germinate as soon as 

 fully formed. 



Concerning the retention of vitality by the resting-spores, Mr T. Goodey and Dr H. B. 

 Hutchinson have recently made a remarkable discovery. Cultures made in 1912 of a Rotham- 

 stead soil which had been sealed up in a dry state since 1846 yielded a quantity of a form of 

 Nodularia turice.nsis. The conditions under which the soil had been kept, and the cultures 

 made, were such that no outside contamination could have taken place, and therefore the small 

 spores of this species (only 7 & by 8 fj.) must have retained their vitality for a period of 66 years. 

 Such spores were indeed resting-spores 



