Development of Cassytha filiformis, L. 413 



Stomata are everywhere present and always in great 

 abundance. On the leaves they are somewhat scattered, 

 elsewhere they are in rows. They are also found on the 

 petals, where they are in short rows. They likewise occur 

 on the walls of the mature fruit, which represent the per- 

 sistent receptacular tube. Cassytha is perhaps unique 

 among the Angiosperms in having the stomata placed trans- 

 versely to the long axis of the stem. The stomata them- 

 selves are rather small and of ordinary appearance. The 

 origin of their transverse position, however, is interesting. 

 On the hypocotyl, in the colorless and succulent region, they 

 are sparse and are placed longitudinally. In the region 

 where it attenuates and begins to look green, they are seen 

 to lie obliquely and at varying and generally increasing 

 angles, until in the green region they lie transversely. Quite 

 young stem tips show stomata developing transversely. 

 The epidermal cells, which in this region are nearly quad- 

 rangular in outline (Fig. 12, a), divide twice in succession, 

 both divisions being perpendicular to the long axis of the 

 stem. This forms four consecutive cells, which are consider- 

 ably broader than they are long, and in cross section decidedly 

 deeper than they are long. All four cells have sharply defined 

 nuclei and a moderate amount of protoplasm. Fig. 12 b, 

 shows this stage. The series of drawings in Fig. 12 is from 

 longitudinal sections of the stem, therefore cross sections 

 of the stomata. Safranin followed by methyl green causes 

 the nuclei to become red or slightly purplish, the cell walls 

 and cytoplasm green. It also stains the later thickening of 

 the guard cell pink. Of the four cells thus formed the inner 

 two are stomatic guard cells, and the further development 

 of the stoma is a mere change of shape. The guard cells 

 expand, squeezing the outer cells somewhat upward, so that 

 they project slightly over the level of neighboring cells, and 

 their nuclei are either much flattened, or they settle into the 

 lowermost portion of the cell, the greatest pressure being 

 upon its middle (Fig. 12, c). 



