576 ABSTRACTS OF MEMOIRS. 



the processes which bring about the formation and the repair of these 

 slits, experiments were undertaken by the author with a view to 

 explaining the reactions and tissue-formations which follow as the 

 result of wounding. It was shown that Laminaria digitata after 

 being wounded reacted rapidly and vigorously. The differentiation in 

 the stem, leaf, and haptera, the age and the corresponding specializa- 

 tion of the tissue cause manifold differences in the regeneration, and 

 the direction and character of the wound also exert an influence. As 

 regards the tearing process, which may be especially well seen in 

 Laminaria hyperhorea, it appeared that these plants slit their leaves 

 autonomously. This is made clear by a microscopical investigation of 

 the leaf surface in the neighbourhood of such a tear. The epidermis 

 at such a place bends inwards from both leaf faces more and more 

 into the inner tissue. One cannot, be it noted, speak of any external 

 wounding. When the epidermis has forced itself in this way into the 

 central tissue the latter finally becomes torn and the further growth 

 of the epidermis closes the wound. From this normal slit-formation 

 and healing we must distinguish the purely mechanical splitting, 

 which heals in exactly the same way as the wounds in the experiments 

 already mentioned. In nature both kinds of slit-formation run into 

 one another. In other Laminarias a similar state of things seems to 

 exist. 



Field observations show that Laminarias have definite requirements 

 as to light, heat, salinity, change of water, etc., at each different age. 

 Differences in the external form of the different parts of the thallus 

 clearly depend upon changes in these conditions. Laboratory experi- 

 ments showed that Laminarias from different localities in the neigh- 

 bourhood of Plymouth possessed different degrees of elasticity, and 

 algae from places where wave movement was slight were stretched, 

 with one and the same load per unit area of section, to a greater 

 extent than the more resistant individuals from very exposed localities. 

 Plants which grew under similar conditions showed, on the contrary, 

 an equal degree of extension. Laminaria digitata stretched similarly 

 to L. saccharina, whilst the surf-loving species L. hyperhorca and bulbosa 



were more resistant. 



K. 



