188 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the genus. She describes the cone, the sporangia, imperfect sporangia, 

 variation in the number of spores in the sporangium, detailed structure 

 of the sporangium wall and mechanism for spore-shedding, the vascular 

 system, and the ligule. She concludes as follows : — " The examination 

 of the species serves to emphasize the intermediate position in which 

 Selaginella stands. On the one hand, it may resort to conditions 

 characteristic of the distinctly primitive Lycopodia, whilst on the other, 

 its wonderful adaptations for cross-fertilization, bringing into play the 

 most elaborate mechanism seen in the Pteridophyte group, and its near 

 approach to the seed habit, render it one of the most interesting as well 

 as instructive genera in the whole of the plant world." 



Selaginella Preissiana.* — H. Bruchmann gives an account of Selagi- 

 nella Preissiana, with a view to showing how far this peculiar species 

 agrees in structure and arrangement of its organs with the other species 

 which he has investigated. He describes the prothallium, the germina- 

 ting plant, the mature plant, the apical growth arising from a group of 

 apical cells, the branching, the stem, leaves, rhizophores, roots. The 

 plant is strongly xerophilous, being well protected against loss of water 

 by means of the conversion of its second dichotomial branch into a sub- 

 terranean rhizome, and by means of the crowding of the shoots which 

 soon produce fertile spikes and which have narrow lanceolate entire 

 leaves, and also by means of the strongly cuticularised epidermis of 

 shoots, rhizome, and rhizophores. 



Origin of Heterospory in Marsilia. t — Oh. Shattuck discusses the 

 origin of heterospory in Marsilia. He gives the following summary of 

 his investigations. 1. The megaspores of Marsilia can be killed by a 

 spray of cold water. They occur only in the oldest sporangia. The 

 plant may then be put under good conditions to ripen sporocarps with- 

 out megaspores. 2. The greatest variations occur when the megaspores 

 and the oldest microspores are killed, and when strong plants develop 

 a few sporocarps out of season. 3. When less than half the spores abort, 

 enlargement does not appear among the microspores ; the surviving 

 spores are larger the greater the abortion. 4. The development of the 

 mother-cells may be checked till the tapetal nuclei completely invest 

 them. A perinium will then form around the mother-cell Wall, invest- 

 ing the four young spores. The sporangium then invariably contains 

 sixteen large forms each containing four nuclei. Or, if growth is less 

 checked, the spores are more or less completely free and vary much in 

 size and shape. 5. Among the young megaspores in a sporangium the 

 contest for supremacy is very evident, several of them assuming con- 

 siderable proportions', but one centrally placed invariably secures the 

 ascendancy. The survivor sometimes retains the aborted members of 

 its tetrad 'attached to its papilla. 6. The enlarged microspores vary in 

 size up to 8 to 1G times the size of the ordinary ones, and the position 

 of the nucleus changes from a central to an apical one (as in megaspores) ; 

 and the vacuolation being more extensive, the shape of the nucleus varies 

 from spherical to oval and finally to meniscus shape (as in megaspore)- 



* Flora, c. (1910) pp. 288-95 (figs.). 



t Bot. Gaz., xlix. (1910) pp. 19-40 (4 pis. and fig.). 



