432 



Minnesota Plant Life. 



While light has a retarding influence upon the growth in 

 length of stems, it has a strong directive influence upon organs, 

 so that they tend to place themselves parallel with the rays, or 

 transverse to them, as their nature may be. It is well known 

 how the lea\'es of geraniums growing in the window turn to- 

 ward the light. Nasturtium vines turn very ([uickly and if 

 one of these plants be put in the window, it will in a short time 

 stretch out its leax'es toward the light and place them vertically 

 to the rays, thus securing a maximum illumination for the 

 starch-making apparatus. Some plants are not thus sensitive 





I'lC. 21(i.— Leaves of the sensitive fern, a shade-loving variety, .\fler photograph by llilibanl. 



to light. For exam])le, such clinfl)ing plants as the ivy or 

 the woodbine do not instinctively bend toward the light, because 

 to do this would tear them from their supports; therefore, they 

 remain either insensible to the directixe influence of light, or 

 they aclually turn Imm it, as do most roots. 



W here tlic liglu is strong and abundant there are often de- 

 x'eloped purple laxeis ( m the under >ides of lea\es to utilize the 

 ^ur])lus light by coiuertnig it into heat and employing it for 

 the growth-energy ot the plant. This is true of such large 



