2-3 



MORPHOLOGICAL DEVE1 DPMENT. 



integration stili more advanced: not simply inasmuch as 

 they unite much greater numbers of morphological units 

 into continuous masses; but also inasmuch as they com- 

 bine the pseudo-foliar structure with the pseud-axial struc- 

 ture. Our own shores furnish an instance of this in the 

 common Laminaria ; and certain gigantic Fuci of the 

 Antartic seas, supply yet better instances. In some of 

 these, the germ develops a very long slender stem, which 

 eventually expands into a large bladder-like or cylindrical 

 air-vessel; and from the surface of this there grow out 

 numerous leaf-shaped expansions. 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, flat- 

 tens out the ends of its subdivisions into fronds 

 like ribands. These, however, are not true 

 foliar appendages, since they are merely ex- 

 panded continuations of the stem. The whole 

 plant, great as is its size, and made up though 

 it seems to be of many groups of mor- 

 phological units, united into a compound 

 group by their marked subordination to a 

 connecting mass, is nevertheless a single 

 thallus. The aggregate is still an aggregate 

 of the second order. 

 But amorg certain of the highest Alga, we do find some- 

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

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

 comparative complexity ; and in addition to pseudo-folia 

 that are like leaves, not only in their general shapes, but 

 in having mid-ribs and even veins ; there are the be- 

 ginnings of a higher stage of integration. Figs. 38, 39, 

 and 40, show some of the steps. In Rhodymenia palmata, 

 Fig. 38, the parent-frond is comparatively irregular in shape, 

 and without a mid-rib ; and along with this very imperfect 

 integration, we see that the secondary fronds growing from 



