A Monograph of the Genns Alarl't. 47 



in the important points in this respect. He distinguishes a margi- 

 nal meristematic tissue at the transition region of the post- 

 embryonal frond, by virtue of which the blade increases in breath. 

 Saugayeau^) discredits the presence of any special tissue which 

 functions for the increase of breadth of the frond and says : — 

 " Le cloisonnement intercalaire dispersé est donc général ; il entraîne 

 l'accroissement en longueur et en largeur de la lamo et il no peut 

 être question de méristème marginal." As far as I have observed 

 in the development of various species of Laminariacese, the growtli 

 in length as well as in breadth of the post- embryonal fronds is 

 due to the activity of the transition region. The region acts for 

 the addition to the length of frond while in its younger stages, 

 and then to the breadth. There is no specialization of tissue for 

 either. The same region acts for both, but more or less separately 

 in time. At the same time, however, it must not be overlooked 

 that the whole part of the blade widens and thickens in itself by 

 cell- multiplication. The areolar arrangements of the epidermal 

 cells, and the changes of shapes of the mucilage glands according 

 to the part of frond, give positive evidence of this fact. Certain 

 differences in the rate of cell- multiplication may be found accord- 

 ing to the parts. The undulation or crispation of the margins of 

 the frond which is quite plane or less waving while young, is due 

 to the greater rate of growth along the margins after the length 

 of frond has been completed by the stipo-frondal growth. The 

 transverse wrinkles along the midrib of Alaria and Undaria, the 

 undulations in the fronds of Costaria and certain Laminaria may 

 be explained in a similar way. The subulate and reflexed tips 

 of the split segments of A. angusta (Plate XV, fig. 2) can hardly 

 be interpreted unless a partial extension of the segments after the 



1) Satjvageatj : Plantules de quelque Laminaires, p. 19. 



