No. ."><>.->] KELPS AND RECAPITULATION THEORY 21 



tinguisliing features of the plant until it reaches a length 

 of about 40 mm. In plants of about this length a few 

 round tubercles begin to appear at the base of the lamina, 

 which has hitherto been smooth as in Hedophyllum. A 

 specimen 75 mm. long (Fig. 30) showed numerous tuber- 

 cles in the transition region, giving it a roughened appear- 

 ance; and there were three instead of two horns below 

 the zone of the tubercles. The basal portion of the stipe 

 was still smooth as in the youngest specimen. In this 

 plant the stipe had elongated scarcely at all and the 

 growth had been restricted to the lamina, which extended 

 through 70 of the 75 mm. of the plant's length. Tubercles 

 similar to those of the transition region had also appeared 

 and these were shown by transmitted light to be connected 

 with streaks of denser tissue running lengthwise through 

 the lamina. 



After this stage, as in Lessoniopsis there is some varia- 

 tion in the age at which the various structures appear. 

 A specimen 18 cm. long (Fig. 33) will serve as an illus- 

 tration of the next step. Here the streaks beneath the 

 tubercles of the lamina had become prominent ridges, 

 much larger than the small tubercles at their summits. 

 The ridges stood out so strongly as to cause depressions 

 on the opposite side of the lamina beneath them. This 

 gave the lamina a wrinked appearance and added greatly 

 to its strength. The margin was entire or slightly undu- 

 late, but at the base were a few short serrations which 

 looked much like the tubercles of the stipe. The rough- 

 ened region of the stipe was about 1 cm. in length and no 

 longer terete like the lower smooth portion, but somewhat 

 flattened. In place of the horns of the younger specimens 

 were several outgrowths, the largest of which bore a 

 small orbicular lamina. The holdfast had become nearly 

 2 cm. in diameter by the great elongation of a few hap- 

 teres. 



In view of the proportions assumed by the adult plant 

 the relation between the lamina and stipe in the juvenile 

 forms is most interesting. In the smallest specimen the 

 lamina is only about three times as long as the stipe. 



