of the secondary segments, takes place by dichotomy or polytomy or, more rarely, 
in a more irregular manner, the growing power of the upper marginal zone ceasing 
at one or more points. KırLLıan has shown (l.c. p. 204) that a cleaving of the 
frond may also take place by longitudinal slits arising under the mechanical influence 
of the waves either accidentally or in certain predestined 
places, much as in the Laminarie. It seems, however, that 
this mode of division is rarely realized in the Danish waters 
where the species never occurs in places so much exposed 
to the influence of the waves as on the rocky shores of the 
Atlantic. è 
Adventitious shoots arise at the margin of the frond 
in autumn and winter and grow out in the spring months 
to new assimilating frond segments. Their number is vari- 
able and their arrangement indeterminate. The segments 
are contracted at the base into a stipe, and this is usually 
so for the apical segments as well as for the lateral ones, 
and they have then all the character of adventitious shoots. 
Sometimes, however, though more rarely, there is only a 
slight or no constriction at the base of the apical segment 
or of the upper portion of the frond that has grown out after 
the last resting period, and the new portion then appears as a = 
direct continuation of the old frond, produced by continued 
activity of the same marginal meristematic zone. Comp. 
fig. 566. Such cases were in particular observed among the \ 
broad fronds growing in harbours and further in repeatedly NÅ 
\ 
dichotomously divided narrow specimens from the Øresund. 
The difference between the new and the old frond is usually É 
very distinct owing to the brighter colour of the first, and N 
often too owing to the presence of organs of reproduction on i 
the latter. IE may happen that the upper portion of the frond / 
dies or is eaten by animals in the course of the first year; 
adventitious shoots are then produced from the cicatrized = 
; : x i ig. 566. 
border of the resting frond. The marginal fronds may  poaymenta palmata. Helle- 
produce new marginal adventitious fronds in the following bk, February (Børgesen). 
int dth > b ated Ed Four generations of shoots are 
winter, an e same process may be repeated once more. FEEDS SE DER 
Three or four generations of shoots frequently occur, from 
which it can be concluded that the frond may reach an age of three or four 
years (fig. 566). The frond often attains a length of 20 cm, more rarely 
24—27 cm (Lille Belt, Øresund). The frond segments of each year usually measure 
10—13.5 cm. 
As to the structure of the adult frond reference may be made to WILLE 
(1891). The marginal meristematic zone at the upper end of the frond does not 
=X 
132 
