52 MORPHOLOGY OP ANGIOSPERMS 



cell. When cauline ovules came to notice, Schleiden, End- 

 lieher, and others took the extreme position that all ovules are 

 cauline, even those evidently parietal upon carpels. This view 

 was opposed by Van Tieghem, 6 Celakovsky, 9 and especially 

 by Warming. 10 The last-mentioned paper is noteworthy for 

 its presentation of the origin and development of the ovule, as 

 well as for its discussion of its morphology. These writers 

 maintained that the ovule is always foliar in origin, and their 

 explanations of cauline ovules are interesting on account of 

 their ingenuity. This view was also maintained by Eichler 

 in his Bliithendiagramme, where an historical resume of the 

 whole subject may be found. The most interesting feature of 

 the whole discussion, however, is the persistent idea- that ovules 

 could not be both foliar and cauline. These last observers, hav- 

 ing established the foliar origin, disproved the bud character 

 of ovules, since the members of leaf-buds arise in acropetal 

 succession, while the nucellus and integuments are basipetal. 

 It was urged that the ovule is a transformed leaf-lobe or leaf- 

 outgrowth, and that this view homologized them with the spo- 

 rangia of ferns. This was a decided step in advance, and it 

 only remained to abandon the doctrine of metamorphosis, and 

 to see that the ovules (sporangia) hold no necessary relation to 

 either leaf or stem, but are themselves long-established and 

 independent members of the plant body, with a history that 

 antedates that of either stem or leaf. 



The length of time from the beginning of megasporangia to 

 their maturity is very indefinitely known, as most investigators 

 do not seem to have kept such a record. It must be extremely 

 variable, as in the case of the microsporangia, and related to 

 the seasonal habit of the plant. In Salix and Populus Cham- 

 berlain' 11 ' found that the megaspore mother-cells are not distin- 

 guished- until the renewal of growth in the spring, although the 

 microsporangia pass the winter in the mother-cell stage; and 

 this lateness of development may be usual in the megaspore 

 series. Enough cases have been observed, however, to show that 

 a much earlier development may often occur. For example, in 

 Acer rubrum Mottier 27 discovered the mother-cell stage in 

 March or earlier, the indication being that this is the winter 

 condition; Chamberlain 39 found the four megaspores of Tril- 

 lium recurvatum fully formed early in April, when the plants 



