. Dansk botanisk arkiv. Plants; Plants -- Denmark. 130 Dansk Botanisk Arkiv, Bd. 3. Nr. Fig. 138. Peyssonnoliä simuläns ). Straight running filaments of the hypothallus. (160:1). direction over the substratum (Fig. 138), 2. Cruoriella with a hypothallus of curved filaments running in little fan-shaped or broad-lanceolate groups over the substra- tum (Fig. 139) and 3. Ethelia with no hypothallus but a mesothallus that gives off branches both downward and upward. This division proved very useful while working out the Peyssonnelia of Dr. Bør- gesen. In his collection species of Peys- sonn
. Dansk botanisk arkiv. Plants; Plants -- Denmark. 130 Dansk Botanisk Arkiv, Bd. 3. Nr. Fig. 138. Peyssonnoliä simuläns ). Straight running filaments of the hypothallus. (160:1). direction over the substratum (Fig. 138), 2. Cruoriella with a hypothallus of curved filaments running in little fan-shaped or broad-lanceolate groups over the substra- tum (Fig. 139) and 3. Ethelia with no hypothallus but a mesothallus that gives off branches both downward and upward. This division proved very useful while working out the Peyssonnelia of Dr. Bør- gesen. In his collection species of Peys- sonnelia and Cruoriella are numerous but the subgenus Ethelia is wanting, it has till now been only found in the East- Indian seas and in the Mediterranean. P. sqiiamaria, the well-known inhabitant of the last-named sea, has a true mesothal- lus though the perithallus inferior is re- duced to only one layer of cells. It is a well-known fact that algæ have a great variability and in how far the Peyssonnelia are subject to this general law, is still an open question, for this group of plants has relatively been little studied. We know that the circular or lobed fronds can be membranaceous (P. rubra), coriaceous (P. sqiiamaria), or calcareous and hard as stone (P. polymorpha), but there are also other forms not entirely calcareous neither coriaceous ; we will have to speak of such a species in the following pages. A frond will, as a rule, increase in thickness by successive division of its ascending filaments, but in the group of P. (Cruoriella) polystrata we find a thick frond consisting of layers of nar- row fronds lying one above the other, creeping continually over each other and forming a thick frond by this mode of growing. Again in another species the frond, after having acquired a certain thickness, splits or tears in a horizontal direction; the lower part decays little by httle, the upper part continues the growth of the frond; its in- ferior cells grow larger, produce rh
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