84 McKenney — Observations on the Development 



In the development of its ovule, Scilla may be said to differ 

 from most plants in having a second macrospore undergo 

 partial germination. In those species which develop more 

 than one embryo-sac, each embryo-sac is developed as a rule 

 from a separate archesporium. In Scilla the rudimentary 

 second embryo-sac is developed from the same archesporium 

 as the normal embryo-sac. Commonly it is the lowest cell of 

 the chain of archesporial daughter cells w^hich becomes the 

 embryo-sac. In Scilla, however, the lowest cell of the chain 

 forms the second rudimentary embryo-sac, while the normal 

 embryo-sac is developed from the cell above this. 



Cytology. 



The larger part of my cytologic study was made on Lilinm 

 as its cells are much larger than those of Scilla. Scilla, how- 

 ever, shows essentially the same cell structure as Liliuin. The 

 cytoplasm of the archesporial cells of Liliwn and Scilla reveals 

 a well-marked reticulum or net-like structure, that of Scilla 

 having the reticular threads more closely woven together. 

 The reticular threads appear to be made up of very minute 

 stainable granules embedded in a less stainable substance. At 

 the point of crossing of the reticular threads there is usually 

 seen a larger granule. In Lilium there can usually be seen a 

 number of small bodies scattered irregularly through the 

 cytoplasm which stain very much like the nucleoli. The 

 cytolymph is comparatively small in amount in archesporia, 

 but gradually increases during development, until it occupies 

 the larger part of the embryo-sac. 



The nucleus is always surrounded by a definite membrane 

 which does not show any pores such as described by Mann. 

 In some cases the chromatin seems to have a loose reticular 

 structure, in others it appears in scattered irregular masses, 

 and in still other cases it has the appearance of a thick twisted 

 thread. The chromatin of resting nuclei has a homogeneous 

 appearance, but during the early stages of mitosis it can be 



