xxx RHIZOPHORA 455 



embryo does not undergo any period of rest, but continues to 

 develop without interruption." 



Though the rest-period is normally non-existent with the seeds 

 of Rhizophora, it has already been observed that it is indicated in 

 rare cases and under exceptional conditions. Thus I have already 

 remarked that in Fiji about one per cent, of the germinating fruits 

 of the American species exhibit more than one seed. These seeds 

 usually begin to germinate about the same time, but in a few cases, 

 say, one in ten, a marked difference in the length of the protruding 

 hypocotyls points to the fact that one of the seeds began to germi- 

 nate some weeks after the other. We at times also meet with fruits 

 which when cut across display two seeds, of which only one is 

 beginning to germinate. Such cases indicative of a pause between 

 the maturation of the seed and the beginning of germination would 

 be very rare. With Rhizophora mangle, probably one in a thousand 

 fruits would be a generous estimate. 



In passing it may be remarked that the same stages occur with 

 Rhizophora mucronata in the development of the seed and in the 

 subsequent germinating process. When the fruit is three lines long 

 the micropyle is but slightly dilated (see figures I and 2). When it 

 is four lines long the endosperm begins to escape from the gaping 

 micropyle and forms a projecting plug. The growth of the embryo 

 now becomes rapid, the endosperm escapes in greater quantity, and 

 by the time the fruit is five lines long the tip of the radicle is on a 

 level with the micropyle, although still covered by the plug (see 

 figures 4, 5, 6). After this, germination begins ; and when the fruit 

 is six lines in length the radicle is in the act of penetrating the 

 plug. Ultimately the tip of the radicle pierces the top of the fruit 

 when this last is nine or ten lines long. As shown in the figures 

 there is continuous growth of the fruit during the maturation and 

 germination of the seed, until, in fact, the plantlet drops into the 

 water. With reference to the stage when germination begins, it 

 should be remarked that the formation of the large plug of endo- 

 sperm outside the micropyle does not necessarily indicate the 

 beginning of germination. Germination is in progress only when 

 the hypocotyl or radicle begins to lengthen and is on the point of 

 piercing the plug of endosperm that fills up the gaping micropyle. 

 This is well shown in this species in the case of fruits with two 

 seeds. Both seeds may have large plugs of endosperm, and yet 

 only one may show indications of germination in the lengthening 

 hypocotyl. 



We must now return to the subject of the growth of the hanging 



