S32 Pub. Puget Sound Biol. Sta. Vol. 2, No. 53 



staining in bulk and afterwards sectioning and mounting. The results were 

 very satisfaetor}-. The material is easy to handle; any good method care- 

 fully followed brings the desired results. Drawings were made with the 

 camera lucida or with projection apparatus. 



Chlorzinciodide was used to determine the composition of the cell 

 walls. Formalin material was rinsed in tap water and the concentrated 

 reagent was applied directly, to flat pieces of the entire thallus, to pieces 

 stripped of the cortical layers, and to sections. The cell walls of both pri- 

 mary and secondary tissues gave the characteristic violet coloration of cel- 

 lulose. Both Soderstrom (1889) and Jonsson (1901) recognize the marked 

 resemblance of the cells of the central cylinder to the sieve tubes of 

 higher plants^ but neither is willling to concede that they are true 

 sieve tubes, though Jonsson figures and describes the pores in the cross 

 walls and the jorotoplasmic connections extending through them. Both 

 chlorzinciodide and Bismarck brown distinctly show the jDresence of 

 callose covering the sieve plate in older parts of the frond, and in younger 

 stages the progressive development of the callose covering is clearly shown. 

 The callose is first formed as a ring at the outer edge,, on both sides of the 

 sieve plate, and gradually extends inward across the plate, finally forming 

 a complete covering, through which, in some cases, the pores can bet traced. 

 The original cell row' of the thallus, then, is a row of sieve tubes, as are 

 all of its branches and their subdivisions. The system of veins which forms 

 a delicate though clearlj'' visible network throughout the fronds of the 

 extremely broad species is thus a system of sieve tubes. 



Desmarestia ligulata, the tjq3e species of the ligulate group, has been 

 used as the basis for study. A detailed description of the formation and de- 

 velopment of the thallus and its various tissues will be given, and the three 

 remaining ligulate species, I), herhacea, D. latissima, and D. foliacea, will 

 be compared with it. 



c. Desmarestia ligulata (Lightfoot) Lamouroux 



(Plate 54, Figs. 1, 2; Plate 62, Figs. 1-7; Plate QS.) 

 Although collected in midsummer, some of the material still bore as- 

 similating hairs, so that all stages in the development of the thallus could 

 be observed, — the structure of the hairs themselves, the intercalary grow- 

 ing region, the beginning of cortication, the development of the axial fila- 

 ment; in fact, the formation and development of primary and secondary 

 tissues from the tip of the youngest thallus branch to the base of the hold- 

 fast. 



Soderstrom (1889) says of the hairs of D. actdeata, "Their cells con- 

 tain much chlorophyll, they are closely and regularly branched, and 

 up to 3 cm. long," In D. ligulata the hairs are very much shorter, be- 



