464 A NATURALIST IN THE PACIFIC chap. 



germination pierces the tissues above it and reaches the floor of 

 the calycine tube. It does not, however, pierce the lining 

 membrane of the tube but pushes it upward until it ruptures about 

 4 millimetres below the base of the style which is carried up with 

 it. Thus a kind of cap is formed, as shown in Fig. 24, which does 

 not fall off from the end of the hypocotyl until it has protruded 

 rather more than an inch. The hypocotyl attains a length 

 varying between 5 and 1 1 inches, the average being about 8 inches. 

 The whole period may be thus divided up : — 



(i) Period between fertilisation and germination 7| weeks. 



(2) Period between the beginning of germination 



and the protrusion of the point of the 

 hypocotyl at the floor of the calycine 

 tube 



(3) Period occupied in the growth of the hypo- ' 



cotyl 8 inches outside the fruit and ter- . 18 

 minating in the fall of the seedling . . . 



I* 



Total 27 weeks. 



The total period of twenty-seven weeks between fertilisation and 

 the fall of the seedling is thus six weeks shorter than that estimated 

 for Rhizophora mangle. On comparing the two tables it will be seen 

 that the difference mainly lies in the length of the second period, 

 namely, that between the commencement of germination and the 

 protrusion of the hypocotyl from the fruit. With Rhizophora 

 mangle the fruit grows considerably in length during this period of 

 the germinating process. On the other hand with Bruguiera 

 rheedii there is, during this period, practically no increase in the 

 length of the fruit, and the radicle has only to penetrate the 

 tissues, 2-?7 lines in thickness, between the seed and the floor of the 

 calycine tube. 



In the mode of separation of the seedling there are very 

 marked differences between this species of Bruguiera and the 

 species of Rhizophora. With Bruguiera rheedii the four small 

 cotyledons, which are united at the base, are, however, left behind 

 at the bottom of the seed-cavity, when the seedling is detached. 

 But there is no expulsion of the seedling, the connection being 

 ultimately severed at the contracted base of the cotyledons inside 

 the fruit. W^hen the seedling is full-sized the nutritive supply 

 begins to fail, and in consequence the pressure of the sides of the 



