DEVELOPMENT. 97 



from the petiole to a single trace and the separation of this again into the 

 central and two lateral traces was seen. The bundles were chiefly composed 

 of procambial cells, though some spirals were present in the three 

 branches within the inner fork. The lamina of the older leaf mentioned 

 had elongated cells along the lines of the veins, but the parenchyma 

 was almost totally undifferentiated and was without intercellular spaces. 

 A leaf of A 7 ! tuberosa richardsoni whose lamina and petiole are each 1.3 cm. 

 long has the air-canals well developed along the midrib. Between the 

 veins the mesophyll consists of five layers of cubical cells arranged in ver- 

 tical lines from the upper to the lower epidermis. The layer next to each 

 epidermis is continuous, but between the vertical rows in the three middle 

 layers long intercellular spaces are present. Iclioblasts are already pres- 

 ent near the midrib. A leaf of N. odorata with lamina 2.5 cm. long and 

 petiole 3.2 cm. has the air-chambers of the mesophyll well marked off by 

 plates of cells ; the palisade consists of a single layer of dense cubical 

 cells, underlaid by two or three layers of flat cells elongated parallel to 

 the surface of the leaf ; the mucilage hairs are large and functional. When 

 the lamina is 8 cm. long the palisade still consists of a single cell-layer ; 

 the big idioblasts have not yet appeared. Stoma mother-cells are present 

 in full number and nearly mature size ; some, indeed, have just divided to 

 form the guard cells. They are round, granular, and highly refractive. 

 The maturation of the stomata occurs only a day or two before the leaf 

 finally expands. Caspary (1854; 1858), in announcing first the apical 

 growth of leaves, showed that this apical growth continues longer in 

 Nymphaea than in other plants, and that the margin of the leaf in all 

 Nymphaeaceae is the latest part to complete its development. 



The tissues of the stem begin to differentiate within 0.25 mm. of the 

 point of apical growth. No plerome is at anytime distinguishable. The 

 lacunar cortex acquires intercellular spaces while all of the tissues are still 

 meristematic, and the early establishment of desmogen strands, adven- 

 titious roots, and external hairs has already been referred to. 



Concerning the development of the flower, we are able to corrob- 

 orate the work of Payer (1857) and Goebel (1886) on N. alba by obser- 

 vations on N. caerulca and lotus, and to add some details. The discussion 

 of important morphological problems will be deferred whenever possible 

 until the observed facts are set forth. The earliest rudiment of a flower 

 that I have seen was a smooth, thimble-shaped upgrowth at the stem apex 

 in N. caerulca. On such a papilla, according to Payer, there appears in 

 N. alba the rudiment of the anterior sepal ; then the two lateral sepals 



8 



