i66 



PART II. — VEGETABLE HISTOLOGY. 



like perforations, technically called sieve-plates, on some portion 

 of their surface. Accompanying them are elongated parenchyma 

 cells rich in albuminoid contents, often called companion cells. 

 The sieve and companion cells, with ordinary parenchymatous 

 elements that may also be present, constitute the soft- bast ; or, 

 owing to the fact that in dicotyledons this region is difficult to 

 distinguish from cambium, it is some- 

 times called cambiform tissue. 



In some forms of this tissue, as in the 

 stem of the Pumpkin, where it is abundant 

 and well developed, the ends of the cells, 

 and not the sides, have the most promi- 

 nent sieve-plates, as in Figs. 427 and 428. 

 In others they are more prominent on the 



Fig. 427. 



Fig. 428. 



Fig. 427.— Small portion of phloem of Pumpkin stem, in transverse section, showing 

 sieve cells, s, represents one of the sieve plates; c, is a companion cell. Magnified about 

 385 diameters. 



Fig. 428. — Longitudinal view of sieve tissue from Pumpkin, s, a sieve-cell: /, a 

 thickened sieve-plate; attached to either surface of the sieve-plate are masses of albuminoid 

 matter, a, shrunken by treatment with alcohol; c companion cell. Magnified about 150 

 diameters. 



side walls than on the end partitions, but not infrequently they 

 occur on both, as may be seen in some of the sieve-cells of the 

 Pumpkin. Sieve-tubes usually contain a thick, slimy, albuminous 

 matter, that is most abundant and dense next to the transverse 

 plates, as shown in Fig. 428, which represents a longitudinal view 

 of sieve-tissue from the Pumpkin stem after having been treated 

 with alcohol. In places the albuminoid matter has shrunken 



