BY JOHN SHIRLEY, D.SC. 63 



plasm. Tliev are .008 mm. in diameter in P. ijlacorhodioides 

 jaid .006 hip. Umhata. (Plate VII., fig. 12). In P. latmima 

 the Cystococcusi (Pleuroicoccus) cells are thickly packed 

 between the necklace-like rows of cells of the superior 

 cortex, and are not more than .004-. 005 mm. in diameter. 

 They are difiicnlt tO' study, as they sieldom show below 

 the cortical threads, which surround and hide them. 



However carefully the tissue may be treated before 

 sectioiiing, maiiy of the algal cells become plasmolyscd. 

 The best killing mixture is chromo-acetic, Schaffner's 

 formula, and the species that permits the best sfcuJy of 

 its gonidia is P. tiliacea. These arei sicattered singly 

 through the thallus, are promptly killed by the solution, 

 and show no relative shrinking of the protoplasm, al- 

 though there is a shrinkage as a.< whole, sine© they no 

 longer fill the hyphal cavity. In the Cystoooccusi cells 

 of this lichen the nucleus and single chlorcplast can be 

 studied. The nucleus usually occupies a central position 

 in the alga, and occasionally bands of protoplasm radiate 

 from it towards the circumference, in which are set rather 

 large chromatophores, presenting an arrangement, more 

 apparent than real, as if they were in circles round the 

 nucleus. 



Algal cells in the act of dividing are not freiquently 

 observed, but they may be^ found by careful searching, 

 and by the fact that two of these cells, or more rarely 

 four, enclosed in the same plexus, have flat surfaces 

 where they face one another. (Plate VI., fig. 9.) 



The best stain for algal cells, as also for licheu 

 spores, is methylene blue. 



5. Rliizince. 



Of the ten species of Parmelia examined, all axe 

 provided with rhizinae except P. i:)lacorliodioides and P. 

 mundata, which belong to the section classified by Ny- 

 lander. Synopsis, p. 400, as "Stirps Parmeliae physodis, 

 Thallusi subtus glaber." 



The rhizinae in Parmeliasi differ markedly from those 

 of their allies the Stictas. In the latter they are composed 

 of comparatively few hyphae, which separate readily, and 

 disclose their ultimate structure of cylindrical cellules, 

 bounded by rather thin walls. These cellules contain 

 the curious protoplasmic pyrenoids, which Willey, Minks, 

 and Jean Muller classed as micro-gonidia. 



In Parmelia the rhizinje are formed of dense multi- 



