A Monograph of the Geuiis Alirla. , 35 



leaving but aggregations of the small basal cells as dark spots on 

 the blade. 



Thus, the hairs in the fronds of Laminariacea^ appear to me 

 to be an absorptive organ as are the isolated hairs in the other 

 Phaeophyceœ. They are localized to form tufts more or less re- 

 sembling in appearance the cryptostoma of Fucacese. The hair- 

 tufts of Laminariace^ie, Dictyotaceœ, Encœliaceae, etc., have been 

 proved to be genetically different from the Fucaceous cryptostomata. 

 Hence, it should be an improper idea to regard the latter as the 

 most advanced form of the hair-tufts. However much they differ 

 from the other Phaeophyceous hairs in their mode of formation, 

 they may be taken equally well as an absorptive organ. In 

 Fucaceœ the sporangia are localized in the hair-pits of a certain 

 part of the frond, called receptacle, the hair-pits in the vegetative 

 parts are named cryptostomata, and those in the receptacles, con- 

 ceptacles. It is quite natural to meet with " the occasional appear- 

 ance of sterile representatives of sexual organs within the crypto- 

 stomata." i) 



In Alaria, the hair-tufts occur on the whole area of both surfaces 

 of the blade, except the stipe, the midrib and the soriferous area of 

 the sporophyll. The transition region of the blade is usually devoid 

 of them, perhaps because all the cells in the area are meristematic. 

 In most cases, certain areas of the blade along both sides of the 

 midrib are also free from them. As the frond develops further, 

 the scars of the withered hair-tufts are stretched in the direction 

 of the expansion of the blade, i.e., parallel to the clefts, resulting in 

 olongated elliptical flecks. The sporophylls of the Metasoria are 

 provided with the hair-tufts wliile they are functioning as vegetative 

 organs, if the blade of the respective frond has them (cfr. p. 25). 



1) Simons : Morphol. Study of Sanj. fiUpendula, p. 174. 



