physiologically cotisidered. 599 



from the veins of detached leaves of Ornithogalum thyrsoideum. 

 Cassini noticed them in the axils of the leaf-stalks of Cardamine 

 pratensis ; M. Hensler, on the points of the leaves of Malaxis 

 paludosa; Meyen, on the inner and outer surfaces of the scales 

 of hyacinth bulbs ; and my colleague, Ludewig, in this garden, 

 on the edge of an oval cotyledon 1^ in. long and | in. thick. 

 The seed seemed to belong to one of the Leguminosae, and the 

 cotyledon itself was broken off by mistake from the young plant, 

 and again put into the ground. 



Lastly, in the fronds of many ferns, bulb-buds of a similar 

 form are produced, such as in Aspidium bulbiferum, Wood- 

 wavdia radicans, Acrostichum flagelliforme. Sec, which cannot 

 really surprise us, as these also bear seed. They appear on the 

 back or on the surface, on the middle or side veins, in the 

 notches of the frond or near the edge, as in Ceratopteris ; but 

 they are always connected with the vessels. Detached leaves of 

 i/emionitis palmata, laid upon moist earth, produce young 

 plants round the edges like Bryophyllum. 



The perfect bulb lasts either one or more years. Perennial 

 bulbs increase yearly, as those of the lily. The annual, or rather 

 biennial, bulb, after it has blossomed, forms a new one by pro- 

 liferations at the side, which, as it increases in size, consumes 

 the old bulb, and is ready to flower the following year. We 

 have an example of this in the tulip. The bulb-tuber, or corm, 

 already mentioned, is a modification of the common bulb. Ac- 

 cording to Link, it arises from the rind of the disk of the bulb 

 becoming exceedingly thick, instead of assuming the leafy 

 form which only appears as thin scales, as in 7'xia, Gladiolus, 

 Crocus, &c. 



The tuber is the last form by which propagation is very 

 readily effected. Tubers are formed from a change which the 

 buds, more or less in number, undergo with the underground 

 stem. The pith, and the outer coat of the stem, increase much 

 in size at the same time; and as many rudiments of buds as 

 there are of the small scaly leaf attached to the parts about to be 

 transformed (which leaf is usually scarcely perceptible with a 

 magnifying glass), so many eyes are formed as rudiments of 

 young plants in the tuber. In this case, the individuality of the 

 bud has been long known ; and hence has arisen the custom of 

 cutting out the eyes of potatoes, and planting them in the ground 

 instead of the whole tuber, by which process each is developed 

 into a young plant, nearly in the same way as a bulb-bud. 

 Potato plants produce their underground stem, from which the 

 tuber is formed, from the base of their main stem ; therefore, as 

 soon as the young plants have attained a certain height they are 

 hoed up, which increases their growth and number. Only those 

 tubers wiiich are formed by the above-described transformation, 



