30 MORPHOLOGICAL DEVELOPMENT. 



into continuous masses, but also inasmuch as they combine 

 the pseudo-foliar structure with the pseud-axial structure. 

 Our own shores furnish an instance of this in the common 

 Laminaria; and certain gigantic Laminariacece of the Ant- 

 arctic seas, furnish yet better instances. In Necrocystis the 

 germ develops a very long slender stem, which eventually 

 expands into a large bladder-like or cylindrical air-vessel; 

 and the surface of this bears numerous leaf-shaped expan- 

 sions. Another kind, Lessonia fuscescens, Fig. 37, shows us a 

 massive stem growing up through water 

 many feet deep a stem which, bifurcating 

 as it approaches the surface, flattens out the 

 ends of its subdivisions into fronds like 

 ribands. These, however, are not true foliar 

 appendages, since they are merely expanded 

 continuations of the stem. In Egregia 

 branches of the thallus not only take the 

 form of leaves, but these are differentiated 

 into several categories in accordance with a 

 division of labour. In any of these Lamin- 

 ariacece the whole plant, great as may be its 

 size, and made up though it seems to be of 

 many groups of morphological units, united 

 into a compound group by their marked subordination to a 

 connecting mass, is nevertheless a single thallus, which is 

 added to by intercalary growth at the " transition-place," at 

 the junction of the stem-like and leaf-like portions. The 

 aggregate is still an aggregate of the second order. 



But among certain of the highest Algce, we do find some- 

 thing more than this union of the pseud-axial with the 

 pseudo-foliar structure. In addition to pseud-axes of com- 

 parative complexity; and in addition to pseudo-folia that 

 are like leaves, not only in their general shapes but in hav- 

 ing mid-ribs and even veins; there are the beginnings of 

 a higher stage of integration. Figs. 38, 39, and 40, show 

 some of the steps. In Rhodymenia palmata, Fig. 38, the 



