ABSTRACTS OF MEMOIRS. 575 



succeeded in getting the swarm spores of Laminaria dirjitata to 

 germinate. First of all there developed a germinal thread consisting 

 of a few cells ; from certain of these cells secondary, one-layered 

 laminae sprouted, which were joined to the germinal thread by colour- 

 less rootlet cells. Later these rootlet cells disappeared, and then the 

 laminae, freed from the germinal threads, developed on their lower 

 sides rhizoids which established a direct attachment to the rocks. In 

 the young plants the cell divisions proceed at first regularly over the 

 whole surface. It is only later that the intercalary growing point is 

 formed between the rhizoids and the leaf; in addition growth tissue 

 develops at the edge of the leaf and makes the extension of the sur- 

 face in breadth possible. Gradually the young plant becomes many- 

 layered ; the outer layers consist of isodiametric, the innermost of 

 elongated cells with rich intercellular substance ; only the point 

 remains for the time one-layered. It must, however, be noted that in 

 the stalk the rows of newly formed central tissue remain near to- 

 gether ; in the leaves, on the other hand, where the growth in breadth 

 strongly predominates, the original longitudinal rows become more and 

 more pulled asunder. A further complication is added, in that (1) be- 

 tween these rows of the internal tissue connections already existed 

 which are now simply mechanically pulled apart, and (2) new connec- 

 tions of this kind are formed. These new connections occur through 

 two cells, which develop at opposite points on the longitudinal rows, 

 growing towards one another and becoming fused. From a cell 

 resulting from such fusion a chain of cells then forms by transverse 

 division. In still later stages the single cells of the longitudinal and 

 transverse rows of the central tissue, whose power of growth ceases, 

 become mechanically deformed through the rapid growth of the leaf. 

 In this way there finally result tube-shaped cells which, according to 

 their age and the degree of the tension to which they are subjected, 

 differ from one another in appearance. We can thus understand the 

 confused mass of cells of all possible shapes which is presented by a 

 section through the central tissue of an old plant. Similar pictures 

 such as one finds in other Laminarias suggest that in them also tissue 

 development takes the same course. 



A point in the anatomy of the haptera is worth noting, viz., 

 that in these there are internally no elongated, tube-shaped cells. As 

 is well known, these algae possess at first an adhesive disc from which 

 the organs of attachment take origin, the construction and shape of 

 the latter being modified by external conditions. 



It is well known that the different representatives of the Laminariae 

 are characterized by regularly split leaves. In order to understand 



NEW SEUIES. — VOL. IX. NO. 4. MARCH, 1913. 2 P 



