92 HICKS, ON GONIDIA OP LICHENS. 



forma indicated at 9 b, each of which consists of a vesicular 

 cell, having an oval mass of bluish-green mucus extending on 

 one side, containing a single or double row of four or five cells, 

 the green contents and mucus not being distinctly separated 

 from each'other. These may develop themselves in the linear 

 direction, as at 9 a, and ultimately pass into Nostoc through 

 the forms indicated at 9 c. Whether they may continue 

 groAving in the linear direction I have no direct evidence 

 to prove, but consider it highly probable. They may also pass 

 directly from the forms at 9 b, to those shown 9 c. The 

 variations, however, are numerous, some consisting of two 

 or three portions united by the vesicular cells. These do not 

 originate from the simpler form at 9 b, but consist of a larger 

 portion of a beaded thread which includes two or more of the 

 vesicular cells. 



Whether the forms at 9 i can arise directly from the 

 Nostoc- or Collema-gonidia without passing into the early 

 condition of a Nostoc, or, in other terms, whether the 

 vesicular cell can arise at so early a period of the change as 

 at 8 a, I have not been able to satisfy myself by direct e\\- 

 dence ; still I have every reason to think it highly probable. 



When these forms are compared with the change which 

 sometimes takes place in the beaded filaments of the Nostoc 

 shown at fig. 10, the similarity of the plan upon which 

 each passes into Nostoc will be sufficiently evident to show 

 how strong a connection exists between Collema and Nostoc. 

 Whether the state of the Nostoc filaments, as shown at 

 fig. 10, should be called a " sporangium " seems questionable ; 

 because, at least in this particular instance, it can scarcely 

 be said to produce spores, that is, free spores. 



At 8 e, is a form in which the cells undergo binary di-\asions, 

 and appear similar to the ceDs of the beaded filaments under 

 a similar condition (fig. 11 a). 



Besides those instances, the gonidia may undergo this 

 Gleocapsoid change within the parent thallus, as I have 

 noticed in the thallus of Cladonia (see Fasciculus II) ; 

 this is by no means a very unusual condition, and is recog- 

 nised easily by the dark-green balls A^isible upon compressing 

 the frond. At fig. 13 is shown a section of a thallus in this 

 state. After a while the thallus bv extrusion, or more com- 

 monly by solution, sets them free, when they assume in some 

 Collemas a Gleocapsa state, the protoplasm being of a very 

 bright green colour, and the mucous sheath colourless and 

 of increased thickness (fig. 13 a). 



In many the subdivisions assume a quarternary form 

 (fig. 13 c), although they may go on to produce large masses 



