356 PLANTS OF NEW ZEALAND 



robusta, p. 282), and many in which the root produces shoots. 

 As a result, it is very often difficult to determine whether a 

 plant structure is a root or stem. Ordinarily, the stem 

 produces shoots bearing leaves, grows upwards, and, especially 

 in herbaceous plants, contains green colouring matter 

 (chlorophyll). On the other hand, the root does not usually 

 produce shoots, does not contain chlorophyll, and grows 

 downwards. These distinctions suffice in most cases, but not 

 in all. Thus, the tuber of the potato is a stem which grows 

 underground, and its shoots are under ordinary circumstances 

 reduced to buds ("eyes"). Many plants have creeping 

 underground stems (rhizomes) e.g., Solomon's Seal. On the 

 other hand, some roots are aerial {v. Dendrobium, p. 124), or 

 produce shoots, e.g., suckers of the white poplar, plums, etc. 

 There is only one point which can be certainly relied upon to 

 distinguish a root from a stem. A root never directly produces 

 leaves. A stem does. 



Now, the roots of the Bhizophora, a tropical mangrove, are 

 not derived from the rootlet of the embryo, but from the stem 

 of the plant — so, on account of their mode of origin, they are 

 termed adventitious roots, i.e., roots not formed in the natural 

 manner. They are obviously used to stay the plant, and give 

 it foothold in the soft mud. Avicennia has few of these 

 supports, but makes use of its roots in a way that is almost 

 unique. Kirk (Forest Flora, p. 272) tells us that, " At low 

 water their naked trunks are exposed, and the mud is seen to 

 be thickly studded with erect shoots from 1 ft. to 3 ft. high,, 

 given off from the tangled roots." He has here fallen into 

 error. The structures described are not shoots, but upward 

 growing roots containing chlorophyll, and are not more than a 

 foot in height. They never produce leaves, and only very 

 rarely fork or branch. They must therefore be regarded as. 

 roots which have lost their most characteristic reaction, and 

 which grow upwards instead of downwards. As they contain 

 chlorophyll, it is probable that they assist in the work of 



