GLASS STRUCTUEES AND APPLIAXCES. 



211 



raised above the top of the pot. When transplanted 

 replace the pots in pans of water, and re-cover them 

 with bell-glasses or hand-lights. If care is taken 

 not to allow air to get into the bell-glasses till the 

 prothallia have ap]Deared, those glasses with a hole 

 through their knobs are preferable to the air-tight 

 ones for this work, as it then becomes easy to air the 

 plantlets without any trouble. 



Recently a very curious anomaly has been dis- 

 covered in the reproductive capacity of Ferns — ■ 

 namely, that of producing prothallia direct from the 

 frond instead of through spores, as is usual. Upon 

 the under side of the frond, and growing out from 

 empty spore-cases, numerous prothallia are seen, 

 from which plants are developed just as when spores 

 have intervened. This singular freak, to which the 

 name Apospory has been given, is as remarkable as 

 if a Pea-plant, instead of producing flowers and 

 then fruit, were to develop pods at once. This re- 

 markable mode of rej)roduction must not be con- 

 founded with that of ordinary proHferousness in 

 fronds, as the latter takes place generally on bar- 

 ren fronds, and moreover perfect plant-buds are 

 formed at once, whereas in Apospory the prothallia 

 are succeeded by the usual fertilising process before 

 plants can be developed. 



GLASS STEUCTUEES AND 

 APPLIAI^rCES. 



GLASS AND GLAZING. 

 By William Colejiak'. 



ALTHOUGH the manufacture of glass dates 

 from a period anterior to the exodus of the 

 children of Israel, more than 3,500 years ago, 

 and was long carried on at Alexandria, whence the 

 Romans were supplied, its application to the glazing 

 of windows in Northern and Western Europe is 

 of comparatively modern date. In the year 674 

 artists were brought over from France to glaze 

 the church windows at Waremouth, in Durham ; 

 and as late as 1567, the use of glass for exclud- 

 ing the cold from palaces and the better class 

 of houses was by no means common, as we learn 

 that the glass casements at Alnwick Castle, the 

 seat of the Dukes of Northumberland, were taken 

 down during the absence of the family to preserve 

 them from accident or injury. A century later the 

 use of vv'indow-glass in Scotland was so small that 

 only the upper rooms in the royal palaces were 

 furnished with it, the lower parts ha\-ing wooden 

 shutters, by means of which the air was admitted or 

 excluded. The manufacture of flint glass in Eng- 

 land was commenced about 1557, but it wrs not until 



the end of the seventeenth century that manu- 

 facturers had made sufiicient progress to become in- 

 dependent of foreigners for the supply of ordinai-y 

 drinking glasses. 



At an early period of its history in this country 

 glass became an object of taxation, and so heavy atid 

 injurious were the duties imposed, that its use was 

 extremely limited until these vexatious imposts were 

 removed by Sir Robert Peel in 1845. Immediately 

 before the removal of the duty there were fourteen 

 manufacturers of crown and sheet glass in the 

 United Kingdom, and they, for want of hands and 

 convenience, at once became overwhelmed with 

 orders. They hired foreign workmen, who, during 

 the transition period, could earn from £4 to £8 a 

 week in the manufactm^e of glass of very ordinary 

 quality. But this in the course of a few years 

 corrected itself. These exciting matters gradually 

 found their level, and the glass trade is ne^^- in the 

 hands of a few influential men, who by their per- 

 severance and energy have out-distanced the 

 foreigner, and have been instrumental in making 

 one of the most important epochs in horticultural 

 history. 



Until the repeal of the duty, forty years ago, 

 and for some time afterwards, there were only a 

 few varieties of glass suitable for horticultui'al 

 purposes ; but by degrees British plate and patent 

 plate were brought into use for the fronts of ornate 

 conservatories. Rough plate, rolled plate, crown 

 and, most important of all, British sheet, were 

 extensively used. One of the worst evils which 

 then sprang into existence was scorching or burning, 

 for which the glass-makers were at one time held 

 responsible ; but it is now j)retty well understood 

 that insufficient ventilation was at the bottom of a 

 great deal of this mischief, as it is quite certain that 

 the glass, however imperfect it' might be, was in- 

 finitely superior to the rough opaque squares which 

 it had so recently replaced. The want of ventila- 

 tion may be readily understood when we consider 

 that small squares, say eight inches by four inches, 

 which admitted a small stream of air at every lap, 

 were displaced by others three feet or more in length, 

 and ten to twelve inches in width. In many old 

 houses every alternate sash-bar was removed in the 

 rapid march of improvement ; but it did not always 

 follow that the ventilating space was increased to 

 admit of an extra supply of fresh air that would 

 compensate for the loss of the hundreds of crevices 

 thus abolished. 



Another difiiculty brought about by this change 

 from small uneven squares to large flat plates, was 

 condensation of moisture. Lender the old system 

 this moisture could escape at every lap. Lender the 

 new system, early morning ventilation — in any 



