A Monograph of the Genns Alaria. J^Q 



less rhombic, if in an oblique direction. In certain species, how- 

 ever, those in the npper portions of the blade are curved or even 

 reflex, not unfrequently ^Yith subulate upper corner. A. augusta 

 shows a remarkable example of this (Plate XV, fig. 2). Very 

 likely this indicates a partial growth in the segments still going 

 on after they have been split. 



Not only in species of Alaria, but in most of the Laminaria- 

 ceous genera, the growth of the frond at an early stage of develop- 

 ment is displayed mainly lengthwise. The full length of the blade 

 is attained while the frond is yet immature. How speedy this 

 growth is may be well imagined from the fact that the enormous 

 length of the blades alluded to above is completed within 3-4 

 months. In this stage, the blade is nauch narrower with the 

 transition region more tapering towards the stem than in the adult 

 form. When the growth in length has more or less retarded, the 

 increase of breadth takes place as a secondary growth. The pro- 

 cess is most remarkable in the transition region, hence the form 

 of the blade undergoes a remarkable change. A blade which is 

 to have a roundish or cordate base in a matured plant may have 

 a cuneate or even attenuating one while in its vigorous growth in 

 length. 1) 



Another factor which influences the shape of the blade of a 

 Laminariacoous species is the movement of water in which it 

 grows. In a quiet bay the blade becomes much thinner and 

 broader than on an open coast ; and on an open coast, a plant 

 grov/ing in a deeper region has broader blades than one near the 

 tidal marks. 



The general statement given above holds good for most species 



1) Yekdo : Three New Marine Algae from. Japan, p. ICO. 



„ Develoi^ment of Costari'i, Undarla, and Lmnmaria, p. 702. 



