446 Messrs Gardiner and Hill, The Histology 



lateral plumule, which is covered and protected by the cotyledonary 

 sheath. After the primary root has attained some length the first 

 leaf of the plumule commences to develope, and, pushing aside the 

 lobes of the cotyledonary sheath, grows upwards with its tip sharply 

 bent over (Fig. 4). The tips of the young leaves and the apex 

 of the plumule are well provided with multicellular hairs, whose 

 cells apparently contain oil. 



At about the same time the tissue just at the junction of the 

 first leaf and the cotyledon divides and forms a small bulb or 

 tuber, which is epicotyledonary in origin 1 (Fig. 5). As germination 

 proceeds the reserve materials of the seed are gradually transported 

 and re-stored as starch in the thin walled cells of the rapidly- 

 enlarging tuber (Fig. 6). The primary root is replaced by adven- 

 titious roots springing from the tuber, which by their shortening 

 is pulled down deeper into the ground ; and finally the first leaf 

 grows out into the air and develops a lamina not unlike that of 

 the mature leaf of this plant (Fig. 7). 



A microscopical examination of sections of the ripe seed of 

 Tamus shews that the hard brown testa consists of an outer layer 

 of flattened cells, within which comes a second layer of deeply- 

 pitted thick-walled cells, elongated in the tangential direction ; 

 but in the vicinity of the micropyle this layer is more prominent, 

 and the cells, which here are elongated in the radial direction, 

 shew a larger number of pits than the corresponding cells in other 

 parts of this layer. The little beak-like persistent micropyle is 

 formed by cells of this character. Within this layer of thick- 

 walled cells comes another single layer, which is succeeded by the 

 thick-walled endosperm tissue (Fig. 3). 



The cells of the endosperm have thick and unpitted walls, and 

 are arranged more or less radially with reference to the centre of 

 the seed. They are filled with aleurone grains, oil, and some small 

 crystals, which, together with the cellulose of the walls, form the 

 chief reserve materials of the seed. No starch occurs in the ripe 

 seed, but soon after germination has commenced a little may be 

 seen in the cells around the embryo, just under the testa. If 

 a section of the young germinating embryo is examined a large 

 number of raphide-containing cells will be seen, which were not 

 visible in the resting condition. These raphides, which apparently 

 consist of Calcium oxalate, occur in the cortical tissue in special 

 cells, which speedily become larger than those around them. 

 The chief seat of deposition of these crystals is the upper portion 

 of the cotyledon and the cotyledonary sheath. In older seedlings 

 they are found in some abundance in the cortical tissues of the 

 roots and leaf. As the depletion of the endosperm proceeds and 

 the seedling increases in size the cotyledon enlarges considerably 

 1 Cf. Bucherer, loc. cit., Le Maout and Decaisne, loc. cit. 



