164 PRACTICAL BOTANY 



2. Colourless, parenchymatous ground-tissue, in which are 

 embedded successively the following : 



3. An outer series of relatively small, sharply circumscribed 

 vascular bundles, arranged in an irregular ring: one larger 

 bundle is usually to be found opposite the lower flattened 

 surface. 



4. An incomplete ring of dark brown sclerenchyma, com* 

 posed of two parts which are usually distinct, viz. an upper 

 strongly curved portion, and smaller flat portion which is 

 nearer the lower surface : small isolated patches of brown 

 sclerenchyma may also be seen dotted about in the ground' 

 tissue. 



5. A central series of bundles, usually two or three in 

 number, and of larger size : they may sometimes be found to be 

 connected at their margin into one irregular ring-like mass. 



Examine the sclerenchyma under a high power, and note the 

 thick, brown, stratified walls : the cells contain a somewhat re' 

 duced protoplasmic body. 



Examine also the parenchymatous ground-tissue, which 

 will be found to consist of cells with thin cellulose walls, and 

 mucilaginous protoplasmic contents, with much starch. Note 

 especially small pegs and rods, which appear as superficial out' 

 growths from the walls adjoining the intercellular spaces. 



Select a single elliptical vascular bundle for detailed observa- 

 tion under a high power, and recognize 



1. The bundle-sheath or endodermis, which is a definite, but 

 narrow layer of cells, with brown coloured contents. 



2. The phloem-sheath or pericycle, which is not quite so 

 definite a layer of deeper cells, with cellulose walls, and 

 plentiful protoplasm. 



3. Within this is a band of phloem, which is wider at the 

 flattened sides of the bundle, but narrower at the two poles : it 

 consists of 



a. Sieve-tubes, which may be recognized by their large 

 cavity, sparing contents, and cellulose walls : note where two 

 sieve-tubes are contiguous that bright yellow granules may be 

 seen adhering to the wall : these indicate the position of the 

 sieve-plates. 



