196 



THE LIFE OF THE PLANT 



29 March 



1882 



In fact, apart from some rare cases, 1 growth in length 

 during an interval of ten to twelve hours is not con- 

 siderable enough to be easily observed, if experimental 

 methods had not stepped in to help us where our sense 

 organs appear to fail. Let us see what are the methods 

 science possesses for demonstrating longitudinal increase 

 in growth, which, owing to its insignificance, escapes 

 immediate observation. We turn for the purpose to the 

 microscope, i.e. we can magnify the object of observation, 

 or use another method which will demonstrate in a 

 magnified form not the plant itself, but simply its motion 



called by us growth. The most 

 convenient microscope for the 

 purpose is the so-called ' solar 

 microscope/ which makes it pos- 

 sible by means of sunlight, or 

 some other sufficiently strong 

 artificial source of light, to throw 

 the image of an object consider- 

 ably magnified upon a screen, as 

 we shall now proceed to do with 

 the root-tip of germinating cress. 

 Once on the screen we shall draw 

 a pencil line round the image 

 and leave the root growing (in 

 water), and return to it at the 

 end of the lecture to see that 

 it has succeeded in growing con- 

 siderably in the interval. Mean- 

 while, here is a figure showing (fig. 55) the successive 

 outlines of a wheat root, observed about every five 

 minutes for an hour. 2 



1 Such are, for instance, the shoots of the bamboo, and the inflorescences 

 of Agave mentioned in one of the previous chapters, which grow several 

 inches a day ; such are also the spiral stalks of Vallisneria, a plant known 

 to all lovers of indoor aquariums (see chapter viii.) 



2 Fig. 55 shows the successive outlines of a wheat root, projected by 

 means of a microscope and a magic lantern. 



5.50 



FIG. 55. 



