A Monograph of the Genias Alaria. 9 



part of the stipe sliows an iiitcrmecliato character between the two 

 parts just answering to its position in a frond. 



In the two-year old stipo, the arrangement of tissues above 

 spoken of remains unaltered in both the complanated and the 

 cylindrical part of the stipe. But a new cortical ring appears 

 between the epidermal layer and the primary cortex. In the 

 cylindrical part it forms a continuous sheath of uniform thickness. 

 In tlie complanated part, it is markedly thickened on both margins, 

 and wing-like ridges on the edges of the stipe are accordingly 

 formed. The midrib has no second-year cortex (Plate XVIII, fig. 

 12-14). 



I have used above the expressions " annual ring " and " second - 

 year cortex " for the stipe of Alaria plants. Wille gives an 

 account of the structure of Alaria esculenta in detail in his Beiträge 

 zur physiologischen Anatomie der Laminariaceen, p. 17, and says: 

 " wiefern wirklich auch das Vorkommen einer solchen Jahresring- 

 bildung bei noch älteren Individuen von Alaria esculenta (L.) Gkev. 

 möglich ist, kann selbstverständlich nach Untersuchung dieses ver- 

 hältnismässig jungen Materiales weder verneint noch bejaht werden." 

 His material is said, according to his estimation, to have contained 

 four -year old plants. I agree with him that what Areschoug^ 

 remarked of Alaria " truncus ima basi 3-4 annulis ornatus " should 

 not be taken as of the annual rings in a similar signification as 

 for the phanerogams. Aeeschoug's description should be taken as 

 simply 3-4 concentric zones of tissues seen in the cross sections 

 of the stipe. I have no doubt, however, that the growth in thick- 

 ness of the stipe of a two-year old Alaria plant is by virtue of 

 the secondary thickening of the pre-existing cortex. The demarca- 



1) Aieîchoug: Observations Phycologioae, V, p. 16. 



