336 W. A. JSetchell — Classification and Geographical 



of unilocular zoosporangia and of unicellular paraphyses. In all 

 the species except those of Chorda and Saccorhiza, the paraphyses 

 possess a peculiar and characteristic hyaline appendage at the tip. 

 The order of the Laminariaceae, then, includes all those species of 

 the Phaeosporese having unilocular sporangia and unicellular para- 

 physes compacted into sori. The plants belonging to it are all of 

 comparatively large size and have the principal meristematic region 

 intercalary. 



When we come to consider carefully the morphology of the vari- 

 ous species of kelp, we soon find that they arrange themselves 

 into three or perhaps four different groups on account of the resem- 

 blances between the methods by which the complexity of form of 

 the adult plants is produced. On careful examination we find that 

 the region of active growth in length, at the transition-place, is the 

 place where these differences arise and that good distinctive charac- 

 ters may be drawn from the different modifications of the transition- 

 places in the different groups. 



Almost any species of JOaminaria represents well the simplest 

 type of all. The stipe expands gradually, or, at times, more or less 

 abruptly, into the blade and the transition-place is plane and un- 

 modified. There is nothing in the external appearance of the transi- 

 tion-place to indicate that at this region, the stipe is increasing in 

 length at its summit and the blade at its base. We may call this 

 type the Laminaria-t^^Q and the special tribe characterized by it 

 the Laminariidese. 



In the J^aminaria-tyi^e we have a very simple and unmodified 

 transition-place and the resulting frond characteristic of the Lami- 

 nariideae is simple and unbranched. But when we turn to the 

 species of the genus Lessonia we find that the adult fronds are pos- 

 sessed of a complexity of structure that warrants us in expecting 

 to find also a more decidedly modified transition-place than we found 

 in Laminaria. In Lessonia, instead of the unbranched frond of the 

 Laminaria, we find numerous small blades borne at the extremities 

 of the ramifications of the dichotomously branched stipe. Conse- 

 quently there are as many transition-places as there are blades. If 

 we examine carefully the different blades of a single specimen, we 

 shall readily discover how the characteristic dichotomous branching 

 of the stipe arises. A longitudinal slit appears in the central por- 

 tion of the transition place at the base of a blade and as blade and 

 stipe increase in length, extends (or appears to) both upwards and 

 downwards until finally we have two blades each with its own short 



