REPRODUCTION OF PLANTS. 91 



is also essential to the welfare of the newly 

 formed plant, and may give the necessary stimu- 

 lus which brings its organs into action. 



70. The fact that darkness is essential to 

 germination has long been known " an em- 

 bryo, exposed to constant light, would not germi- 

 nate at all, and hence the care taken by nature 

 to provide a covering to all embryos in the form 

 of the integument of the seed, or of a pericarp." 

 Mr. Hunt has recently turned his attention to 

 this subject, and he remarks thus on it : " It is 

 not at present in our power to explain in any 

 thing like a satisfactory manner the way in 

 which the luminous rays act in preventing ger- 

 mination. The changes which take place in the 

 seed during the process have been investigated 

 by Saussure : oxygen gas is consumed, and car- 

 bonic acid gas evolved ; and the volume of the 

 latter is exactly equal to the volume of the 

 former. The grain weighs less after germination 

 than it did before ; the loss of weight varying 

 from one-third to one-fifth. This loss of course 

 depends on the combination of its carbon with 

 the oxygen absorbed, which is evolved as car- 

 bonic acid. According to Prout, malted and un- 

 malted Barley differ in the following respects : 



