BUNTON: TOWNSENDIA EXSCAPA. 193 



found in a single mesophyll cell of a number of plants, as given 

 in Haberlant's "Pflanzen-Anatomie" : 



Spongy 

 Palisade cells, parench. cells. 



Fragaria elatior 86 14 



Pulmonaria officinalis 85 15 



Ricinus communis 82 18 



Brassica rapa 80 20 



Galeopsis tetrahit 79 21 



Ft'opaeolum majus 77 23 



Helianthus anmms 73 27 



Phaseolus vinltiflorus 69 31 



Bellis perennis 67 33 



When compared with the plants above mentioned, it is seen 

 that in the leaf of Toivnsendia the chloroplastic surface is 

 relatively small. On both sides of the leaf the number of 

 chloroplasts in a single mesophyll cell is approximately 

 twenty-nine, thus giving to both sides of the leaf the same 

 chlorophyll-producing volume. The small number of chloro- 

 plasts found in the mesophyll cells of the upper side allows 

 the sunlight to penetrate to the lower side of the leaf, thus 

 giving to the cells there the power to carry on photosynthesis 

 more effectively. 



The Water-storage Tissues. — In the leaf of Townsendia 

 there is an admirable arrangement for all the mesophyll cells 

 to have immediate access to water. Throughout the full 

 length of the leaf on both sides are found large cells which 

 are used primarily for the storage of water. These water- 

 storage cells, however, seem to assume other functions; they 

 evidently take part in the conduction of water and aid to a 

 slight degree in photosynthesis. They have very thin walls, 

 which are lined by a few chloroplasts much smaller than those 

 found in the other mesophyll cells. Bordering on these water- 

 storage cells are mesophyll cells which draw upon them for 

 water when there is need. 



In order to secure the greatest access to water the palisade 

 cells occur in various relations : bordering on veins, on water- 

 storage cells, on spongy parenchyma cells. In the following 

 table is shown the relative frequency of palisade cells bor- 

 dering respectively on water-storage cells, veins and spongy 

 parenchyma cells : 



Boi'dering on water-storage cells 222 



Bordering on veins 81 



Bordering on spongy parenchyma cells 42 



