10 " ENDEAVOUR " SCIENTIFIC RKSULTS. 



form, which is also the commonest, and Avhich may average 

 about three-quarters of au inch in height, tin- whole of the pinnae 

 may be composed of internodes bearing a single pair. Generally, 

 however, from two to four pinnae, about the centre, may have a 

 couple of pairs on the first internode, but on no others. So, as 

 the hydrophyton is more robust, we find a larger proportion of 

 the internodes supporting two or more pairs. In the largest 

 specimen which I have in a preparation I find one of the median 

 pinna? with four pairs on the first internode, two each on flu- 

 second, third, and fourth, and one on each of the other eight. 

 The nearest pinna on the opposite side has one internode with 

 four pairs, two with two pairs each, and ten with one pair. No 

 other pinna commences with more than three pairs. It is very 

 probable that in larger specimens the development of the longer 

 internodes may be carried still further. 



It may be observed, in regard to >. elonyata, that in these 

 distinctions there is rro question of a mere difference of age. 

 The robust forms aie on a larger scale than the others from the 

 root up, the hydrothecae being in proportion to the general size 

 of the polypidom. Further, it is evident that the ultimate 

 height is approximately determined by the time the shoot is half 

 grown, for Ave find that only a very few pinnae about the middle 

 reach the maximum development, the succeeding ones then 

 commencing to diminish. 



In fairly large specimens of >S. marplestonei the most ordinary 

 arrangement is for the longest internodes to bear four, or even 

 five pairs, then folloAV from one to three iuteruodes of two pairs 

 each, and finally from one to five or six with only one pair. In 

 other parts of the same specimen the first internode may hear 

 two or three pairs, and all the rest one pair ; and an internode 

 of the second order often comes between two of the first. There 

 seems more tendency than in 8. elonyata- for the longer 

 iuternodes to persist nearly to the end of the pinna?. I have not 

 met with specimens corresponding with the smallest forms of 

 8. eluiiyata, in such it might be expected that internodes of the 

 first order would be more prevalent. 



In 8. bideas the habit is similar to that of S. maplestonei, 

 but in such specimens as I have seen the tendency is towards 

 shorter internodes, and in a small specimen all the internodes, 

 with very few exceptions, are of the first order. 



S. pulchella has the arrangement much the same as the last. 



In S. 1/1,'nn nat.a many pinnse consist mainly of internodes of the 

 second order, others almost entirely of single pairs. 



In the commonest form of S. inucrocarim all the interuodes 

 may have a single pair only, but in other specimens internodes 

 of the second order prevail throughout. 



