SECT. I 



MORPHOLOGY 



99 



tive period the calli are dissolved. They also generally disappear from 

 sieve-plates that have ceased to be functional. 



A more complete fusion of protoplasts is found in the formation 

 of laticiferous vessels {*'^). These have the same contents as latex 

 cells (p. 80). Their occurrence, like that of latex cells, is limited to 

 a few distinct plant families, such as the Papaveraceae, of which the 

 Poppy {Papaver) or Celandine {Chelidonium), with its characteristic 

 orange-coloured " sap," are familiar examples, or the Corapositae, of 

 which in particular the Lettuce (Laduca) may be cited. Latex vessels 

 are distinguished from latex cells only by the method of their 



Fio. 107. — Tangential section through the peri- 

 phery of the stem of Scorznn era hispanica, sliow- 

 ing reticulately united latex vessels, (x 240.) 



Fig. 108. — Lower third of a scalariforra 

 vessel from the rhizome of the common 

 Bracken Fern, Pteris aqwUina. t, Trans- 

 versely elongated pits in the lateral walls; 

 g, scalariform perforations of the terminal 

 wall. (After de Bary, x 95.) 



development, which has resulted from the fusion of rows of elongated 

 cells, the separating transverse walls of which have become more or 

 less completely absorbed. Such vessels as a rule possess lateral 

 branches, which, on meeting with one another, fuse by the absorption 

 of their end walls (Fig. 107). The mucilage tubes (^^) which are 

 found in many Monocotyledons present points of resemblance to the 

 laticiferous vessels. Their mucilaginous sap contains albumen, starch, 

 glucose, and tannins in addition to inorganic compounds. 



A cell fusion also takes place in the formation of vessels or 

 TRACHEAE, but it should not be considered as a union between living 

 cell bodies, but merely as one between cell cavities. The mature 



