280 MacMillax: Observations ox Xereocystis 



haptercs attaclicd to the bottom and so strong are the stipes. In 

 the late autumn the Ncrcocystis dies, for, as long- a^^o noted bv 

 Mertens, while one of the largest of the algae it is an annual. 



Histology. — The intimate structure of the Lamlnariaceae has 

 commanded the attention of many careful observers. Among the 

 more important papers that I have consulted may be mentioned 

 those of Postels and Ruprecht (1840), Ruprecht (1848), Thuret 



J 



J 



7 



5\ 



Wille (1885. 1897), Kjcllman (1883, 1893), Grabcnd6rfer (1885), 

 Oliver (188;), Rosenthal (1890), Setchell (1891), Guignard (1892), 

 Murray (1893). Few of these make aii)- mention of Ncrcocystis, 

 but since in details of structure the genera of the Lamlnariaceae 



are rather similar, all these papers and several others have been of 

 assistance. 



In general, as particularly demonstrated by Reinke and Wille, 

 the Lamlnariaceae have well-marked tissue-areas which ma)- be re- 

 garded as In a degree physiologically equivalent to those of higher 

 plants. Cortex and central cylinder arc distinguishable in stipes 

 and laminae. Mestome, stereome, tegumentary and photos\-n- 

 thetic areas are well differentiated although the second, to which 

 Setchcll's sclerenchyma of Saccorhiza may belong, is poorly de- 

 veloped as \w most hydrophytes. 



The primitive Disc. — Longitudinal sections of a primitive disc 

 belonging to a plant 18 mm. in length showed it to be irregularly 

 ch-cular in shape, .8 mm. in diameter, .1 mm. high. Near the 



center of the upper side arises the stipe with a diameter of 75 mic. 

 The primitive disc consists of parenchymatous tissue of approxi- 

 mately Isodiamctrlcal polyedral thin-wallcd cells about 12 mIc. In 

 diameter. The superficial la}'cr is made up of much smaller epl- 

 ■ dermal cells similar to those which occur over the stipe and lamina. 

 The layer of cells which is apprcssed to the substratum — in this 

 case the surface of a Zostcra leaf— are for the most part similar In 

 shape to the general fundamental tissue of the disc but not much 

 more than half as large. Some of these appressed cells are pro- 

 longed into stocking-shaped rhizoids the flat surfaces of which lie 

 very close against the epidermis of the eel-grass. Measurements 

 of some of these stocking-cells showed them to be 7 mic. in diam- 



