POLYSIPHONIA 387 



disturbed at certain points by dark spherical bodies, 

 which lie embedded in the tissue below the pericentral 

 cells : these are the tetraspores. 



2. That they decrease in size as the apex of the 

 branchlet is approached. 



3. That they have no clearly definite arrangement. 



4. That each undergoes a division into four, hence the 

 term " tetraspore." 



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 Florideae, still in Callithamnion the mother- 

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

 remain undivided. 



In 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 

 recognized 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 



c c 2 



