POLYSIPHONIA. 43 



5. That they escape by rupture of the layer of peri- 

 central cells: note in older parts the vacant cavities 

 whence tetraspores have escaped. 



6. That the mature tetraspores are naked, spherical, 

 and motionless protoplasmic bodies. 



By a careful comparison of tetraspores in early stages of 

 development it may be ascertained that they originate from 

 cells of the central series, as shortly-stalked bodies, of which 

 the head enlarges and divides into four, while the pedicel remains 

 small. 



Though the term " tetraspore " is strictly applicable in this 

 case, as in most of the Floridese, still in Callithamnion the mother- 

 cells may undergo a variable number of divisions, or may even 

 remain undivided. 



Jn many forms, with simple structure of the thallus, the 

 tetraspores may be produced externally, as in Callithamnion^ 

 Ptilota, &c. 



VIII. As above noted, the male plants may be 

 recognised by the presence of yellowish tassels of 

 antheridia, which are to be found mature from the 

 beginning of April onwards : late in the season the ends 

 of their branches become ragged and irregular. Mount 

 as before a small piece of a male plant taken in April, 

 and observe under a medium power 



1. The normal structure of the main thallus. 



2. The club-shaped antheridial branches, often 

 associated together in groups : each consists of 



a. A unicellular pedicel, by which it is attached 



to the thallus. 

 &. A central linear series of cells, which is almost 



entirely hidden by 

 c. Numerous, closely aggregated, and small 



antheridial cells. 



