234 



THE AMERICAN MONTHLY 



[December, 



complete, unless additional rings 

 are run on for a finish. 



In making the rings on slides it 

 is not always easy to make the edges 

 true, and sometimes the cement 

 spreads too far. In such cases I 

 turn them down with the point of 

 a knife until they suit. If the 

 cement is taken just at the right 

 time this is easily done, and it im- 

 proves the appearance very much. 



Albekt H. Chester. 



The Stem of Pumpkin for 



Illustrating Plant 



Histology.* 



The stem of the common pump- 

 kin {Cucurbita Pepo) is admirably 

 adapted for use in the laboratory to 

 illustrate many kinds of cell-sti-uct- 

 ures, and the larger part of the 

 tissues of the higher plants. It is 

 of a convenient size to be held for 

 sectioning, and after remaining in a 

 sufficient quantity of strong alcohol 

 for awhile becomes very solid, so 

 that exceedingly thin sections are 

 easily obtained. The cells are com- 

 paratively large and a power of 250 

 to 500 diameters will demonstrate 

 almost every detail. 



A cross-section of the stem shows 

 without magnification five small 

 fibro-vascular bundles lying beneath 

 the five angles of the stem, with 

 the same number of much larger 

 bundles situated between them, but 

 deeper. These are imbedded in the 

 fundamental tissue, and the whole 

 surrounded by a cortical rind. The 

 centre of the stem is hollow, due to 

 rupture of the fundamental tissue 

 from expansion by growth. Other 

 features of the stem can be made 

 out without a microscope, but it is 

 best to revert to them after their 

 full significance is understood. 



An enumeration of the kinds of 



* From The Botanical Gazette. 



cells and tissues to be met with will 

 answer the purpose of this notice, 

 as no extended description is in- 

 tended. The cortical rind is com- 

 posed of epidermis and hypoderma. 

 Three forms of cells belong to the 

 epidermal system — simple epider- 

 mis cells, hairs, and guard-cells of 

 the stomata, the latter best studied 

 in cross-sections of the stem. The 

 fundamental system comprises the 

 large-celled, thin walled parenchyma 

 in which the fibro-vascular bundles 

 lie, and the hypodermal tissues. 

 The parenchyma is colorless and 

 varies little except in size of the 

 cells. The hypoderma consists of 

 two layers, encircling the stem, 

 partly performing the office of im- 

 parting strength, and partly con- 

 taining assimilative protoplasm. The 

 innermost of these is of uniform 

 thickness and made up of slender 

 wood-cells. Thin transverse septa are 

 occasionally met with, which are 

 usually regarded as subsequent 

 formations, but may be, however, 

 the persistent partitions of cells that 

 generally coalesce completely to 

 form single wood-cells. The wall of 

 the cells is differentiated into three 

 lamellae — a middle one, with one on 

 either side — and has simple pits not ; 

 penetrating the middle lamella. 

 These pits are twisted in such a way 

 that they have the appearance of 

 being situated at the intersection of 

 the arms of an oblique cross, when 

 seen in front view. To determine 

 their stracture requires careful ex- 

 amination with a high power. Be- 

 tween the wood-ring and the epider- 

 mis lies a ring of tissues of very 

 considerable importance, but not 

 homogeneous like the last. It con- 

 sists of parenchyma containing 

 chlorophyll, in which lie numerous 

 masses of collenchyma in contact 

 with the epidermis but not extend- 

 ing quite deep enough to come in 

 contact with the cortical wood. The 



