126 GENERAL BOTANY 



and thus have a very different organization and mode of life. 

 We shall thus secure not only a summary of the principles already 

 learned but also a fundamental study of the relations which 

 plants sustain to their environments. 



AN ANNUAL: THE GARDEN BEAN 



The bean plant is typical of the most abundant and common 

 forms of plant life that live in medium conditions on land. It is 

 likewise representative of the so-called annual plants, which com- 

 plete their life cycle in a single season and then die down, leaving 

 the seed as the wintering and hibernating structure to perpetuate 

 the race the next season. The life of an individual bean plant 

 for a season (Fig. 64) will thus give us a general idea of the 

 seasonal life and activities of common annual land plants. 



Food storage. As indicated above, the seed is the wintering 

 stage of the bean plant and is composed of an embryo plantlet 

 in which is stored an abundance of food for the growth of the 

 embryo until it becomes self-supporting. This food, however, is 

 stored up in the bean in the form of solid grains of starch and 

 protein. Fats are also stored in a condition unsuitable for imme- 

 diate use by the embryo. In order that the growing embryo 

 plantlet may use this solid food, therefore, it must first be trans- 

 formed into soluble foods by digestion. 



Digestion and respiration. Digestion in the bean is not very 

 different from the same process carried on in a growing animal 

 fed upon beans, whole or ground into meal. In the case of the 

 animal the digestive juices are poured into the digestive tract 

 and mixed with the food in the stomach and intestine ; in the 

 bean seed the cells of the cotyledons in which the food is stored 

 secrete the digesting substances or ferments, which transform 

 the solid starch and protein into soluble sugar and protein. The 

 fat is likewise ultimately transformed into sugar before being 

 used by the growing plantlet. In Fig. 63 these facts are graphi- 

 cally illustrated in connection with the cotyledons of a growing 

 bean seedling. In such a seedling the life processes are unusually 

 active, as in animals. The reason for this is that growth in the 



