456 A NATURALIST IN THE PACIFIC chap. 



seedling of Rhizophora mangle. We have already remarked 

 that, as shown in the Table, about fifteen weeks (107 days) is the 

 average time elapsing between the fertilisation of the ovule and the 

 protrusion of the tip of the radicle through the top of the fruit. A 

 further period of seventeen and a half weeks (122 days) is occupied 

 by the growth of the seedling on the tree, at the end of which 

 period it drops into the water or mud according to the state of the 

 tide. This gives a total period of nearly thirty-three weeks (229 

 days) as the duration of the time between fertilisation and the fall 

 of the seedling. This may be divided, as has been already implied, 

 in the following manner : — 



'£> 



(i) Period between fertilisation and germination. 9 weeks. 



(2) Period between the commencement of germi-] 



nation and the protrusion of the tip of the r 6^ weeks, 

 radicle through the top of the fruit. -' 



(3) Period occupied by the growth of the hypo-] 



cotyl outside the fruit, and terminating in r 17} weeks, 

 the fall of the seedling from the tree. -' 



Total . . -33 weeks. 



This represents the average of numerous observations, the devi- 

 ations being from two to three weeks on either side. In the latter 

 part of its growth, the lower end of the hypocotyl becomes thickened 

 or club-like, and during the last week or ten days the increase in 

 length is arrested altogether. 



My observations on the growth of the seedling on the tree of 

 Rhizophora mucronata were comparatively few ; but, as shown in 

 the Table on page 453 they give nearly the same rate of growth. 

 Taking the average length attained by the hypocotyl on the tree at 

 sixteen inches, and employing as well the data supplied by Rhizo- 

 phora mangle, a period of 26|- weeks would elapse from the time 

 the hypocotyl pierces the top of the fruit until the plantlet falls 

 from the tree. If we then add, as in the case of the other species, 

 1 51 weeks for the preceding period between fertilisation and the 

 protrusion of the hypocotyl, we get a total of 42 weeks for the 

 whole period from fertilisation to the fall of the seedling. In the 

 extreme cases where a length of almost two feet is attained on the 

 tree, the period would somewhat exceed twelve months ; and in 

 those rare instances in other regions, when, according to Schimper, 

 the seedling is a metre in length, probably eighteen months would 

 be required. The period for Rhizophora mucronata is thus con- 



