68 THE AMERICAN" MONTHLY [Mch 



especially as compared with the frequency of the bundles 

 in the central cylinder ; the endodermis, whether homo- 

 geneous or heterogeneous, the shape and thickening of 

 its cells ; the frequency and arrangement of the fibro-vas- 

 cular bundles of the central cylinder, the relation of the 

 phloem and xylem to each other ; the cells of the funda- 

 mental tissue and their contents, and the presence or ab- 

 sence in it of intercellular space. In the Pteridophyta, 

 in addition to characters which are indicated by what has 

 already been said, attention should be directed to the 

 characters of the endodermis and the pericycle. The 

 limits of an article do not permit of all the various details 

 of microscopical analysis being dealt with fully, so it will 

 perhaps suffice to mention one or two other classes of 

 slides, and the method of examination to which they 

 should be subjected. Leaf sections should be examined 

 with a view to observing if the leaf is of the bi-facial or 

 centric type ; the epidermis of the upper and lower sur- 

 faces should be compared, the size, form, and thickening 

 of the individual cells being noted, the presence of hairs, 

 glands, and stomata, as well as the size and other charac- 

 ters of the same should be observed. Attention should 

 be directed to the palissade cells, if present, their form 

 and location; to the remaining parenchyma of the meso- 

 phyll, whether closely or loosely compacted, and the na- 

 ture of its contents. The presence of hypoderma should 

 be particularly recorded, as should also the presence, lo- 

 cation, and characters of other sclerotic cells. Crystals 

 and specialized receptacles, such as oleo-resin and tannin 

 sacs, should be noted. The fibro-vascular system must 

 be examined to ascertain whether it is restricted to a cen- 

 tral strand only, or is accompanied by laterial ones. In 

 connection with this system should be observed the rela- 

 tion to each other of the phloem and xylem, and the pres- 

 ence of stereom in the form of a continuous or discontin- 

 uous sheath. As a type of other classes of slides, starch 



