GLASS STRUCTURES AND APPLIANCES. 



43 



influence of wind. Cells of this character form the' 

 bulk of timber and of fibrous matter like hemp or 

 flax. (Fig. 33.) 



Vessels. — Vessels constitute another modifica- 

 tion of cells, generally elongated, and with one 

 or more fibres coiled up in the interior. These 

 fibres are deposits from the protoplasm, similar 

 to the woody matter, but not spread in layers 

 over the whole inner surface of the cell. The fibre 



GLASS STRUCTUEES AND 

 APPLIANCES. 



BELL-GLASSES, CLOCHES; HAND-LIGHTS. 



THE fickleness and severities of our climate com* 

 pelled the horticulturist to have recourse to 

 protecting structures of some sort or other at very 

 early times. The higher the culture and the more 

 beautiful and valuable the plants grown, the greater 



m 



m 



Fig. 33.— Woody 

 Fibre, magnified. 



Fig. 34.— Spiral Vessels between 

 Pith-cells and Wood-cells. 



Fig. 35.— Striated and Puuctated 

 Vessels of Melon. 



may readily be seen by breaking across a leaf-stalk 

 of the Strawberry, when the fine fibres may be 

 pulled out. They either form complete coils, or 

 are broken up into sepaiate fragments, producing an 

 appearance of more or less regular bars, or pits, the 

 pits being really the interspaces between the ends of 

 the bars. All true flowering plants have spiral ves- 

 sels (Fig. 34) . Ferns are remarkable for the posses- 

 sion of scalariform vessels, in which the bars are so 

 regularly arranged as to resemble the rungs of a 

 ladder. Usually they require the aid of the 

 microscope to render them visible. The vessels vary 

 in character in diflterent cases, but it is not neces- 

 sary for our purpose to go into further detail. 



the need of such structures to protect them from 

 sudden destruction. Hence the growing demand 

 for more glass," and better glass, may be said to 

 have run parallel with the advancement of horticul- 

 ture. Several counter-influences, however, checked 

 that demand. Among these the more potent were, 

 that its use was but imperfectly understood, its price 

 was high, its quality inferior. It was not until the 

 excise duty on glass was swept away that it was set 

 free and made fit for horticultural purposes. Long 

 before the era of Crystal Palaces, however, glass — 

 albeit it was mostly green rather than white — was 

 more or less freely used for horticultural purposes. 

 The vital importance of shelter without shadow was 



