289 



a complete nutrient solution, they at once formed a meristem on their outer 

 edges by repeated cell-division, while the starch supply decreased. 



The distribution of the sexual organs varies according to the nutritive 

 conditions. Ameristic prothallia bear only antheridia, never archegonia, 

 which are associated with the presence of a meristem. Of special impor- 

 tance at this point is Prantl's observation that ameristic prothallia of Os- 

 munda, which had borne isolated antheridia, developed abundant archegonia 

 after nitrogen had been supplied ; besides the archegonia, antheridia also 

 appeared. 



From these changes produced by the nutritive substances is explained 

 without forcing the tendency to "dioecia" ascribed to some ferns by 

 various authors ; by Millardet^ for Osmunda, by Bauke- for the Cyatheaceae 

 and for Platycerium, and by Jonkmann^ for the Marattiaceae. 



H. Hoffman* cites further notes pertinent here ; first of all, Von Hof- 

 rneister, who assumes that in Equisetum the prothallia produce decidedly 

 more antheridia in the light and in a dry locality, i. e., bear more male plants 

 since the prothallia are almost entirely dioecious. 



•Borodin found that germinating spores of Allosurus Sagittatus de- 

 veloped antheridia when placed in the dark. 



The Production of Sterile Blossoms. (Sterility.) 



Sterile blossoms in phanerogams are due primarily to a lack of nitro- 

 gen. This may manifest itself in very different ways ; as already mentioned 

 in the blasting of grain, a sufficient supply of nitrogen may be present in 

 the soil but as result of a prolonged, intense drought there is lacking the 

 carrier, the water, to bring to a further normal development the already 

 differentiated stamens and pistils. On the other hand there may be in heavy 

 seeding a struggle for nitrogen in which the plants that earliest attain most 

 vigorous vegetative development take the nutriment from the less vigorous 

 ones. In a consideration of sterility there must further be taken into ac- 

 count the cases where the existing nutritive material is used up in some 

 other way, so that a one-sided increase or decrease of a growth factor favors 

 the vegetative utilization of the elaborated organic material to such an ex- 

 tent that nitrogen sufficient to mature the sexual organs is lacking. Finally 

 it not infrequently happens that the material is abundantly used in the de- 

 velopment of the lesser nitrogen requiring male organs and no longer 

 suffices for the development of the ovary. The cases among phanerogams 

 where starvation conditions induce blossom development are not in opposi- 

 tion to this view. Examples of this are found in our fruit trees, where dis- 

 eased specimens with a pronounced decrease of shoot development "bloom 

 themselves to death." In horticultural practice plants are purposely starved 

 in order to attain flower production (Kantua dependens, Correa. etc.) 



1 Pring-shelm's Jahrbiicher, X, p. 97. 



2 Bot. Zeit. 1878, p. 757. 



3 Extrait des Actes du Congr&s international. Amsterdam, 1877. 



4 Hoffmann, H., Zur Geschlechtsbestimmung. Bot. Zeit. 1871. Nos. 6 and 7. 



