74 FLORA HISTORIC A. 



*' There is no great danger in taking off the 

 glasses for a few minutes or half an hour, when 

 it is cloudy, and the air rather warm and moist ; 

 but if no opportunity of this kind occur in due 

 time it should be done early in the morning, and 

 rather than to omit doing it entirely, it will be 

 better to take the glasses off, if it is only for five 

 minutes, turning them upside down upon the path, 

 in order to air them, and replacing them again 

 over the plants ; even this will be of great ser- 

 vice, though not equal to a more effectual airing 

 at favourable times, which, indeed, becomes 

 more frequently necessary in proportion to the 

 length of time the pipings have been upon the 

 bed ; but when once they begin to strike fibre, 

 they will soon spindle up and become extremely 

 weak, if not carefully attended to, agreeably to 

 the following directions: when their fibres are 

 formed, which the additional verdure and growth 

 of the plants will demonstrate, the glasses should 

 be placed over them very lightly, in order that 

 more air may be admitted, and when they be- 

 come tolerably well rooted, the glasses being no 

 longer necessary, should be entirely taken away, 

 but it seldom happens that all the plants, under 

 the same glass, strike root together ; some are 

 generally a few days or a week forwarder than 

 the rest, as will be apparent by their superior 



