1890-91.] On Vegetable Ivory. 461 



in shape, or rather like the quarter of a sphere. It is protected 

 by a dark-brown testa, very dense and hard, measuring 1-3 0th 

 of an inch in thickness or thereby, and broadening out to half 

 an inch at the hilum, where it is perforated by mucilage pores. 

 There is an almond-shaped cavity near the centre of each nut 

 which detracts from its commercial value, but serves an im- 

 portant purpose in the life-history of the plant. When the 

 embryo, which is small and situated near the hilum, begins to 

 germinate, the cotyledon finds room for growth inside the 

 cavity ; it absorbs the endosperm for its first nourishment, and 

 while this absorption of stored-up albumen is going on, the 

 radicle and plumule find their way through a fracture in the 

 testa, and begin the struggle for existence. The extreme 

 hardness of the seed frequently causes an observer to remark 

 that germination cannot be possible ; but it has to be borne 

 in mind that in their native soil dispersion must take place 

 while the albumen is in a comparatively pulpy condition, and 

 soaking in water has a softening effect even on very old 

 fruit. 



Microscopic examination of the endosperm shows that it is 

 built up of polygonal cells radially arranged, ha\dng lignified 

 walls and radiating pores, with a sucker-like expansion next 

 the cell-wall but no intercellular spaces. Their structure is 

 best seen when the section is mounted dry. If a seed be cut 

 in halves, and the flat surface well polished, one can easily 

 see with the naked eye a series of circular markings, which 

 somewhat resemble dentine, and so justify its popular name 

 of vegetable ivory. These circles seem to indicate that the 

 endosperm is built up of concentric spheres ; but microscopic 

 preparations show, as already stated, that the cells are laid 

 down radially, and the rings are probably due to the thicken- 

 ing of the transverse cell-walls. 



The testa is deserving of careful examination, as it exhibits 

 various forms of well- developed sclerenchyma. It will be re- 

 membered that Mr Coats read a paper last session, entitled 

 " On Sclerenchymatous Cells," and T would refer members to 

 that communication for an account of their structure and 

 functions ; but it may be repeated here that these cells are 

 never directly concerned in the living processes of plant-life, — 

 they form a purely mechanical tissue. The relative positions 



