Olson: OHSERVATIONS ON GIGARTINA. 155 



Holdfast. — The holdfast is disc-like, and varies in size accord- 

 ing to the number of plants springing from it. In an isolated in- 

 dividual (Fig. 3, PI. 13) it is seen to be but little larger than the 

 circumference of the base of the stipe. On the under side, by 

 which it is attached to the substratum, it is seen to have a smooth 

 surface, and two areas are clearly distinguishable in the alco- 

 holic material used in this study; a central, nearly circular al- 

 most translucent area, and an outer apparently denser portion 

 (Fig. 3, PI. 13). When viewed from the upper side the signi- 

 ficance of these areas is understood. If a large holdfast be ex- 

 amined, from which part of the fronds have been removed, the 

 upper surface will be seen to be uneven and dotted with circu- 

 lar pits bordered by very distinct rims (Fig. 6, PI. 13). On 

 running the point of a needle through one of the translucent 

 areas of the under side it is found to correspond with the pit of 

 the upper side. A still more interesting demonstration is to pull 

 away one of the fronds still attached to the holdfast. If this be 

 done carefully it will be seen that a characteristic pit remains to 

 mark the point of attachment of the stipe. An old holdfast is 

 found to be covered with these scars, which are very perfect 

 markings of the outline of the stipe at the point of attachment. 



Stipe. — The stipe is a well-marked organ whose presence 

 is more or less evident in all the plants, especially as they attain 

 their mature size. Some of the members of the group in Fig. 

 I, PI. 13, show that in the first stages the width of the frond 

 varies but little from the base to the tip, so that a distinct stipe 

 is scarcely distinguishable. Very soon, however, the upper por- 

 tion of the frond begins to expand and a typical stipe becomes 

 evident. Its outline just at the point of attachment to the hold- 

 fast is circular, but above this it becomes slightly compressed in 

 one diameter so that its cross section appears oval or elliptical. 

 The transition trom stipe to lamina is so gradual that no distinct 

 demarcation can be detected between them. The shorter diam- 

 eter becomes still shorter, and the longer one increases to the 

 width of the frond till all appearance of the stipe has van- 

 ished and even the greater thickness at the center of the lamina 

 merges so gradually into the thinner margins that it cannot be 

 be said to be present as a midrib. 



Lamina. — The lamina is seen to attain its greatest width at 

 some little distance from the tip. If it is branched the division 

 is dichotomous, though the lobes are often unequal in size, and 



