68 



FIRST GROUP. THALLOPHYTES. 



Sphacelarieae from its segments. It is remarkable that in some species (Sph. tribuloides 



and Sph. cirrhosa} short branches 

 drop off from the thallus as gem- 

 mae, and that single cells in these 

 gemmae develope into creeping 

 filaments, on which new shoots 

 of Sphacelaria are produced as 

 lateral branches. The Sphace- 

 larieae too not unfrequently have 

 hair-structures with an intercalary 

 growing-point, and there are also 

 species of Ectocarpus with creep- 

 ing primary filaments on which 

 other sporangiferous filaments are 

 produced as lateral axes ; the 

 growing-point in these creeping 

 filaments is likewise terminal. 

 The position of the growing-point 

 therefore gives no clear distinc- 

 tion between the two groups of 

 Phaeosporeae,nor does the higher 

 differentiation of the tissue in the 

 Sphacelarieae, for we have seen 

 this exhibited in Giraudia sphace- 

 lartozdes, one of the Phaeosporeae 

 which is closely allied to the 

 Ectocarpeae. 



c. The LAMINARIEAE * occupy 

 a peculiar position in the series. 

 They are among the plants which 

 attain the greatest length in the 

 vegetable kingdom, as was stated 

 above. Their thallus has a stalk 

 of greater or less length, made 

 fast to a substratum by root-like 

 attachments which cling tightly 

 to stones, stems of other Algae 

 and the like, and ending above 

 in a flat divided or undivided 

 lamina. The stem in some spe- 

 cies is of considerable thickness ; 

 in L. Cloustoni and L.flexicaulis 

 it is not unusual to find stems 

 with a diameter of three centi- 

 metres, in the Lessonieae it is 

 said to reach twenty. This arises 

 from the fact that the stem pos- 

 sesses secondary growth in thick- 

 ness, which takes place in a me- 

 ristem beneath the rind, which is 



FIG. 43. Laminarta Cloustoni, a. specimen engaged in renewing its 

 lamina, about 3 times less than the natural size ; s stalk ; TV root-like 

 organs of attachment (some of their extremities cut oft) ; e zone of vegetative 

 growth ; b' new lamina, which has already begun to split at c, and has split at d; 

 b the old lamina above the new; the old decays and is cast off. 



1 Le Jolis, Examen des especes confondues sous le nom de Laminaria digitata, suivi de quelques 

 observations sur le genre Laminaria (Nov. act. acad. Leop. Carol. 1855, comptes rendus 1855). 

 Janczewski, Observations sur 1'accroissement du thalle des Pheosp. (Mem. de la soc. nat. de Cher- 

 bourg, T. XX, 1875, p. 13 of the reprint). 



