146 Transactions. 



The phloem forms a continuous ring round the xylem ; the phloem 

 parencliyma cells contain small starch -grains. The xvlem forms a band 

 only slightly wider than the phloem ; it consists of vessels and of wood- 

 fibres. 



The i)ith consists of thin-walled more or less circular cells, with small 

 air-spaces between them. The cells adjacent to the xylem are small, and 

 contain starch. There is a large pith-cavity. 



17. Epilobium pubens A. Rich. 



Growth-form. — The plant is a small herb, with stems 3-8 in. high, 

 slender, simple, decumbent and woody at the base, erect above, terete, 

 uniformly clothed with a short fine pubescence. The leaves are alternate, 

 \-l in. long, ovate, obtuse, narrowed into slender petioles, pubescent on 

 both surfaces, thin and toothed. 



Anatomy. 



Leaf. — This is thinner than in E. pedunculare, and the veins are more 

 prominent. The upper epidermis is formed of large cells, more or less 

 rectangular in transverse section ; the walls are thin, except the external 

 ones, which are somewhat thickened. A thin cuticle is present. Some of 

 the epidermal cells are produced into unicellular hairs, which contain proto- 

 plasm and which have thin cutinized walls. The lower epidermis is similar 

 to the upper, except that the cells are smaller. Stomates are confined to 

 the lower surface, where they are very numerous. The guard-cells are 

 small, and are slightly raised above the surface of the epidermis. 



The palisade tissue is composed of 2 rows of thin-walled cells closely 

 packed together, so that there are only very small intercellular air-spaces. 

 These cells contain chloroplasts, which are smaller and much less numerous 

 than in E. 'pedimculare. 



The spongy tissue consists of about 4 rows of more or less rounded thin- 

 walled cells, which are somewhat loosely arranged. Raphides of calcium 

 oxalate are present in the mesophyll. Many of the mesophyll cells, especi- 

 ally those of the palisade tissue, contain drops of oil. Canals are present, 

 as in E. pedunculare, but they are more numerous. 



The vascular bundles are larger than in E. pedunculare, and the xylem 

 contains more lignified elements. Around and below the bundles is a 

 water-storage tissue, which consists of thin-walled, polygonal, closely packed, 

 colourless cells. 



Stem (fig. 10). — ^The epidermis consists of small oval or rectangular cells, 

 with all walls thickened and with a fairly thick cuticle. Many of the 

 epidermal cells are produced into straight unicellular hairs, w^hich contain 

 protoplasm and have thin cutinized walls. Stomates are not numerous ; 

 they are level with the epidermis, and the guard-cells are small. 



The outer layers of the cortex (about 3 rows of cells) consist of oval 

 cells, with their walls slightly thickened and with small intercellular air- 

 spaces. These cells contain a few chloroplasts, and some of tliem contain 

 oil. The rest of the cortex consists of larger more irregular cells. The 

 endodermis is well marked, and is composed of a layer of large cells with 

 thin suberized walls. 



The phloem forms a narrower band than in E. pedunculare, and the 

 xylem is wider, but is of the same type. 



