312 BOTANY PART i 



2. Such a well-nourished mycelium on being transferred to pure 

 water proceeds completely and at once to form sporangia. 



3. In solutions of leucin (O'l per cent) and haemoglobin (O'l per 

 cent) at first a strong growth develops and then sexual organs are 

 formed. Swarm-spores are not formed ; they appear, however, after 

 the sexual organs, when a more dilute solution (O'Ol per cent) of 

 haemoglobin is employed. 



It is thus clear that quite definite conditions exist for vegetative 

 growth, others for the formation of sexual organs, and yet others for 

 the appearance of asexual reproduction. 



Conditions of the Formation of Flowers. In the Phanerogams 

 asexual reproduction by means of bulbils, etc., is much less prominent 

 than the sexual reproduction which is connected with the flower. 

 The question of the causes of the development of flowers is of 

 special interest. Observations in nature and experimental work 

 show that in this case also sexual reproduction is not absolutely 

 essential to the maintenance of the species, and that the formation 

 of flowers only takes place under quite definite conditions. The 

 results which KLEBS obtained with Sempervivum Funkii can be sum- 

 marised thus : 



1. With active carbon -assimilation in bright light and rapid 

 absorption of water and nutrient salts, the plant continues to grow 

 purely vegetatively. 



2. With active carbon -assimilation in bright light, but with 

 limitation of the absorption of water and salts, the development of 

 flowers takes place. 



. 3. With a moderate absorption of water and nutrient salts it de- 

 pends on the intensity of the illumination whether vegetative growth 

 or the production of flowers takes place. With weaker intensity of 

 light, and when blue light is used, only growth takes place ; with 

 stronger illumination or with red light flowering occurs. 



KLEBS distinguished three phases in the formation of the flowers 

 of Sempervivum. 1. The establishment of the condition of readiness for 

 flower-development. 2. The formation of the primordia of flowers 

 recognisable under the microscope. 3. The enlargement of the in- 

 florescence. These three phases are connected with wholly different 

 conditions and depend therefore in different ways on external factors. 

 The initial condition is determined by a preponderance of carbon- 

 assimilation over processes in which carbohydrates are consumed, such 

 as respiration and vegetative growth. Since a high temperature 

 increases the respiration and nutrient salts promote vegetative growth, 

 a low temperature and a limited supply of nutrient salts are necessary 

 in addition to good illumination to render the plant ready to develop 

 flowers. This condition when once attained may be destroyed by a 

 high temperature, while it may be preserved for a long while, even 

 in darkness, by a low temperature. While in this respect 'light 



