Cook: Potamogeton lucens 215 





my figure 7, his figure 25 with my figure 8 y and his figure 24 with 

 my figure 9. It is well known that there may be considerable varia- 

 tion between genera of the same family and also some variations 

 between species of the same genus. This question of the variation 

 and constancy of characters between closely related species, genera, 

 and families is of sufficient importance to demand the attention of 

 students of this subject. 



That this large nucleus of the nucellar tube performs a very 

 important function in the nourishment of the endosperm and 

 embryo appears self-evident at this stage of our knowledge. The 

 writer has previously discussed this phase of the subject in papers 

 on Nymphaeaceae (4, 5). Its morphological significance is some- 

 what uncertain. In my first paper on Nymphaeaceae (4) I ex. 

 pressed the opinion that this might, be of some importance in 

 determining the close relationship of the Nymphaeaceae with mono- 

 cotyledonous plants in the series Helobiae. The phylogenetic 

 importance of these morphological characters was denied by John- 

 son (11) but since that time the family Piperaceae, on which he 

 made his studies, has been placed by the taxonomist as the lowest 

 of the dicotyledonous families. The writer believes that we do 

 not have sufficient data to draw very definite conclusions but 



wishes to emphasize the importance of further studies in these 

 famili 



les. 



The Embryo 



The general development of the embryo is in accordance with 

 the Alisma type and bears a very striking resemblance to the 

 embryo of Sagittaria variabilis. The young embryo increases in 



-figures a, b, c). A 



{fe< 



the first division of the embryos of Potamogeton foliosus and 5. 

 variabilis occurs earlier than in the embryo of P^luccns. After 

 the first division the basal cell grows rapidly and forms a very 



Z an niche Ilia. Naias 



very similar to the basal cell of Sp 



Putamogeton foli- 

 {fignres 15, iS, 2j). It contains an abundance 

 °f protoplasm, stains deeply, and gives every evidence of great 

 activity until the appearance of the cotyledon, when it first shows 

 signs of disintegration. 



