250 



The Garden Magazine, June, 1922 



PART OF A SAHUARO FOREST NEAR TUCSON, 

 ARIZONA 



Including several trees of Carnegia gigantea, 

 a massive succulent which stores up literally 

 tons of water in its great club-like trunks 



through the walls and membranes of cells. The 

 gum is so weakly osmotic that its pull is difficult 

 to measure and it does not pass the walls of a cell. 

 If the sugar we sprinkle on our strawberries were 

 changed into gum, we would become quickly aware 

 of the change. Such an alteration does take place 

 in the plant which lives in places of extreme 

 drought and this change is responsible for the di- 

 rection in which many groups of plants have de- 

 veloped. 



atoms of hydrogen and 1 1 of oxygen may lose hydrogen and oxygen in the form 

 of water when the cells are dried, and the molecule is rearranged as a pentose 

 or 5 carbon sugar, which is further condensed to the pentosans or mucilage 

 which is not at all sweet to the taste. 



Some pentose and some of its condensation product, the pentosans, are 

 always present in the cell. These substances play an important part in 

 growth. The notable increase which follows desiccation converts so much 

 common sugar to mucilage that the physical qualities of the latter determine 

 the fate and character of the cells and tissues. 



No matter how much of the ordinary type of sugar might be formed in the 

 cell, it would readily diffuse out through the walls and to other organs of the 

 plant. Not so with the mucilage. When it is formed from the more soluble 

 sugar as a result of drought it must remain in the cell in which it is formed, 

 and while it cannot pull water into this cell with any great force yet it imbibes 

 and holds all of the water that does come into the cell by other causes when the 



drought is over expanding the cell by its 

 swelling power. This result is the essen- 

 tial feature of a succulent such as the 

 Cactus, enlarged thin-walled cells, dis- 

 tended with mucilage and the imbibed 

 water. (See Coralluma pictured on pre- 

 ceding page.) Thus in studying the 

 leaves of a Castilleja which had become 

 succulent, the cells were seen to be three 

 times as long as in other leaves which had 

 not undergone this transformation. 



The drying out of cells converts com- 

 mon sugars to mucilages, and these sub- 

 stances are traps which imbibe and hold 

 water which may later come into the cells. 

 This is the cause of the succulent, and 

 such action may occur in the individual 

 plant ordinarily thin-leaved. It has 



SKELETON OF SAHUARO 

 (CARNEGIA) 



Despite the fact that the main stem is 

 dead, the Sahuaro stores up such large 

 reserves of food and water that the single 

 living branch attached on right is able to 

 prolong its solitary existence for the space 

 of a year or two, even forming flowers 

 and maturing fruit 



NOW turn to the cells of the green plant which 

 are actively engaged in processes starting in 

 the leaf and resulting in the formation of sweet 

 sugars. These sugars slowly diffuse through stems 

 and branches, undergoing conversion into starches 



in some organs or tissues, being acted upon by ferments in other places, but in no place 

 exerting any discernible effect upon the general size or character of the cells or tissues. 



If the cane sugar or glucose which found its way into a cell or a mass of growing 

 cells should be abruptly changed into a gum with the implied alterations in physical 

 action, it may be readily seen that the cells which are loaded with the mucilaginous 

 material would act in a manner different from that which would be shown if they held 

 only common sugar. 



Such a change does occur when a mass of cells loses water beyond a certain propor- 

 tion. The sweet hexose sugars which have 6 or multiples of 6 atoms of carbon, 12 



THE BARREL CACTUS (ECHINOCACTUS) 



A canny prospector takes advantage of ready-made 

 opportunity and, after beheading the plant, squeezes 

 the juice from its white inner pulp to quench his thirst 



