THE MEGASPORANGIUM 53 



were not more than 5 centimeters high, and the embryo-sac of 

 Hepatica ready for fertilization while the ground was still 

 frozen; we have seen embryo-sacs of Epigaea ready for fertil- 

 ization in the autumn, pollination probably occurring the fol- 

 lowing spring ; and Schaffner 56 has found that in Erythronium 

 the archesporial cell begins to enlarge about the first of October 

 and nuclear changes occur, and that by the first of December the 

 nucleus is very large and the mother-cell stage reached, which 

 persists until early spring. The subject should be investigated 

 especially in connection with vernal herbs and early blooming 

 shrubs and trees. 



The details of the development of the ovule have been ad- 

 mirably given by Warming 10 and Strasburger, 13 supplement- 

 ing and correcting the earlier observations of Hofmeister, 4 ' 5 

 and the literature since has grown so extensively that full cita- 

 tion is impossible (Fig. 21). At first the epidermis of the mem- 

 ber upon which the ovule is to appear is even, and in the hypo- 

 dermal layer the archesporium may or may not be evident. A 

 slight protuberance is developed by cell-divisions, which are 

 usually only radial in the epidermal layer, resulting in a more 

 extended plate of cells; but in the hypodermal layer they are 

 variable, resulting in a mass of tissue, or in many cases in but 

 a single axial row of cells. In any event, the protuberance 

 becomes more and more prominent and constitutes the nucellus 

 of the nascent ovule. 



After the nucellus has become prominent, an annular out- 

 growth begins at its base, and with greater or less rapidity 

 develops into the inner and often only integument, in most 

 cases overtopping the nucellus (Fig. 3, 7). In case there is an 

 outer integument, its annular primordium becomes visible soon 

 after the inner integument is well under way (Fig. 21). If the 

 aril be placed in this category, it has been observed that this 

 third integument arises much later than the other two, usually 

 after fertilization, as in Asphodelus, Aloe, Nymphaea, Podo- 

 phyllum, Euonymus, Celastrus, Myristica, etc., although in all 

 these cases its point of origin does not seem to be well estab- 

 lished. Disregarding the aril, two integuments seem to be the 

 rule among Monocotyledons, the only recorded exception we 

 have noted being Crinum, although, doubtless, there are others. 

 Two integuments prevail among the Archichlamydeae also, the 



