ISTichols, A morphological study of Juniperus communis var. depressa. 227 



from the jacket cells into the egg cell is impossible. They suggest 

 tliat "the jacket cells are glandulär or secretory and render the 

 storage food of the endosperm soluble and available for the de- 

 veloping egg". According to Chamberlain (1906), in many 

 cycads the egg "receives food material through haustorial pro- 

 jections which are in direct contact with the cytoplasni of the 

 jacket cells". But among the Cupresseae the conditions are very 

 different from those found in snch groups as the Cycadales and 

 Abieteae. There each archegonium is completely enveloped by a 

 layer of jacket cells, while among the Cupresseae only the outer- 

 most archegonia of the group are in contact with the jacket layer. 

 Yet, as Lawson (1907 b) clearly points out, "the cytoplasm of 

 the centrally situated egg cells shows very little difference in the 

 character and quantity of food granules from that of the egg cells 

 in contact with the jacket cells". Lawson therefore believes that 

 "all food substances carried into the egg are translocated in soluble 

 form", and that "the transference of food substances from egg cell 

 to egg cell is the same as that from jacket cell to egg cell". 

 During their later history the jacket cells mJ. communis, asnoted 

 by Noren (1907), are frequently binucleate (flg. 95), and while 

 in some cases the nuclear division which gives rise to this con- 

 dition may be amitotic, as Noren afürms, the frequent presence 

 of mitotic figures in the jacket cells as late as the time when the 

 proembryo is being developed would indicate that thesenuclei are 

 ordinarily produced in the usual manner. 



The nucleoli and pseudonucleoli. — Probably no struc- 

 tures in plant or animal cells have been the subject of more dis- 

 cussion, yet withal are more incompletely understood, than nucleoli. 

 The term nucleolus has been applied so indiscriminately by different 

 writers to various structures both inside and outside of the nucleus 

 that it has come to have a very vague meaning, and a thorough 

 comprehension of the different bodies thus designated and of their 

 relation to the metabolic activities of the cell would doubtless illu- 

 minate many cytological problems which are at present inexplicable. 

 It is not the purpose of the writer to enter upon a discussion 

 of the nucleolus, except in so far as it directly affects the more 

 general phenomena under consideration, but, in view of the large 

 number of nucleolus-like bodies which are found in the egg nuclei 

 of gymnosperms, it seems best at this point to consider these 

 structures briefly as they appear in J. communis depressa. 



In the microspore mother cell there is always present a con- 

 spicaous nucleolus which takes the chromatin stains and seems to 

 be more or less intimately associated with the reticulum. During 

 the nuclear changes which precede the heterotypic division this 

 body graduaüy loses its affinity for dyes and at diakinesis has 

 literally faded from view, apparently without having undergone 

 any change in shape. Coincident with the Separation of the 

 daughter chromosomes toward their respective poles there appear 

 in the region of the spindle minute droplets, the so-called extra- 

 nuclear nucleoli, which react slightly to stains, but which usually 



15* 



