FOKMATION OF CELLS^-TISSUES 



319 



lost its fluid contents, the neighbouring parenchymatous cells 

 protrude through the pores which exist in its wall, and then 

 multiply in its interior by division, forming a cellular mass 

 which may completely fill it ; to this intra-cellular tissue 

 the name of tilllen or thyloses has been given. It may be 

 well observed in the wood of the Oak, in that of Bohinia Pseud- 

 acacia, in Periploca, and in the stem of Gucumis sativus. 



b. Spifal Vessels. — This name is applied to vessels with 

 tapering extremities, having either one continuous spiral fibril 

 running from end to end, as is commonly the case {fig. 684), or 

 two or more librUs {fig. 685) running parallel to one another. 

 The latter kind are well seen in the stem of the Banana 



Fig. 689. Fig. 690, KiG. 691. 



d 



/''if/. 688. Piece of an annular yessel from Zea Mays. 

 h. The thin cell-wall ; r, the annular thickening of 

 the cell-wall ; r', vertical section of one of the rings, 

 showing I/, the inner substance, and i, the denser 

 layer over tTie inner side of the ring projecting into 



the cavity of the cell. After Sachs. Figs. 689, 



690. Annular vessels. Fig. 691. Vessel showing a 



combination of rings and spiral fibres. 



and other allied plants, in the young shoots of the Asparagus, 

 and in the Pitcher Plant. The fibril contained within the 

 spiral vessel is generally so elastic as to admit of being uncoiled 

 when the vessel is pulled asunder. This appearance may be 

 commonly seen by the naked eye by partially breaking the young 

 shoots, flower-stalks, or leaf-stalks of almost any plant, or the 

 leaves of the Hyacinth, Banana, and others, and gently pulling 

 asunder the two ends, when the uncoiled fibrils appear like a 

 fine cobweb. In most cases the coils of the fibril are close 

 together, so that the enclosing membrane cannot be observed 

 between them ; but in other instances they are more or less 

 separated by portions of membrane {fig. 686). 



Spiral vessels occur in the earliest differentiated portions of 



