344 MALE PERN. 



(a) On the cut transverse surface, note that the actual 

 stem portion is relatively small, the greater part of the 

 thickness being made up by the leaf -bases ; the ground- 

 tissue contains starch and gum. Test the ground-tissue 

 with iodine, then cut a fresh surface and apply aniline 

 sulphate, which will bring out clearly the vascular 

 bundles, arranged in a ring both in the stem itself and in 

 each leaf -base. 



(Z>) Next, cut the upper portion of the shoot in halves by 

 a slice passing through the centre as nearly as possible, 

 including the growing tip, and note that the thickness of 

 the stem is practically uniform throughout its length. 

 The large central bundles run, on the whole, longitudinally, 

 but have an uneven course. By scraping away the ground 

 tissue, you can see that these bundles form a network, and 

 that smaller buddies run from the large central stem- 

 bundles into the bases of the leaves. 



(c) The course and arrangement of the two sets of 

 bundles can be made out rather better by cutting off tan- 

 gential slices, starting from the outside ; note that each 

 mesh of the central network corresponds to the insertion 

 of a leaf, and that the bundles passing out into the leaf 

 come from the margin of the mesh. Each mesh is there- 

 fore called a " leaf -gap " or foliar gap. 



483. "Vascular Skeleton." Prepare a "vascular skeleton" 

 of the stem, as follows : With a blunt instrument or a hard brush, 

 clear away the ground tissue from the piece of stem that has been 

 soaked (or boiled for a short time) in dilute acid. The skeleton re- 

 sembles a piece of wire netting rolled up into a tube, the leaf- 

 bundles arising as branches from the larger central bundles of the 

 tube at the edges of the diamond -shaped meshes or leaf -gaps. 



484. T. S. of Pern Stem (Fig. 84). Owing to the 

 bulky nature of the stem and the curved course of the 

 bundles in it, the microscopic structure of the bundles is 

 more easily made out by cutting sections of the leaf -stock. 

 Cut transverse sections of the stem (or leaf-stalk), 

 mount some unstained in glycerine, others treated with 

 iodine, others treated with aniline sulphate. 



