Lecture XX VI L 241 



If the bulb be split down longitudinally it will be seen that the 

 leaves and outer scales are attached to a low cone- or cushion- 

 shaped mass of tissue tougher than that composing the leaves. 

 This is the stem and from its broad base the roots spring. The 

 flowering stern is a prolongation of this cone. In the angle of the 

 uppermost foliage-leaf of the cone is a bud which will develop into 

 the flowering stem of next year. Its base will form a bulb which 

 will be coated over with the remains of the leaves of the current 

 season. 



The roots have a structure similar to those of the Buttercup. 

 The conducting tract occupies the axis and is enveloped in a thick 

 cortex. This distribution of tissues evidently has relation to the 

 external conditions to which the root is subjected.^ It has to 

 follow a tortuous course among the soil particles ; hence the axial 

 location of the conducting tract built up of elongated overlapping 

 elements, such as would resist longitudinal stretching forces, is 

 rendered necessary. The cortex, being composed of thin-walled 

 cells, each of which may be distorted owing to the elasticity and 

 ductility of its cell- wall, can accommodate itself to local compressions 

 and is consequently suitable to occupy the outermost position. As 

 in the Buttercup, the woody strand of the conducting tract has the 

 form of a grooved core ; the grooves and ridges on this core are, 

 however, more numerous. The crests of the ridges are occupied 

 by the filaments of protoxylem, while the rest of the core is composed 

 of primary wood, consisting principally of tracheids and vessels with 

 some wood-parenchyma interspersed between. The bast forms fine 

 strands lying in the grooves of the woody core. It is composed of 

 sieve-tubes and companion-cells. A single layer of undifferentiated 

 cells the pericycle forms a sheath over the conducting tract. 

 From cells of this layer new roots are formed. They originate 

 opposite one of the protoxylem-filaments and shove their way out- 

 wards through the surrounding cortex. When they emerge at the 

 surface the ruptured cortex forms a collar at their base. The 

 cortex resembles a thick sleeve covering the conducting tract. It 

 is formed for the most part of rounded thin-walled cells, including 

 between them angular intercellular spaces. It is bounded on the 

 outside by the piliferous layer, which is a superficial layer of cells, 

 some of which grow out at right angles to the surface and form 

 absorbent hairs. They are very thin-walled. Their walls are lined 

 with a very delicate film of protoplasm which in turn encloses a 

 large watery vacuole occupying the larger part of the cavity of the 

 cell. Their thin walls mould themselves to the surrounding soil 

 particles and often adhere closely to them. On the inside the 



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