INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 121 



B. CRYPTOGAMIA. 



Cryptogamia Vascularia. 



Influence of Light on the Bilateral Structure of the Prothal- 

 lium of Ferns.* — The cause of the bilateralness of the prothallia of 

 ferns has already been much discussed by Bauke, Leitgeb, and others.f 

 To the literature of the subject Prantl now adds another important 

 contribution. The mode of experiment adopted by him was as follows. 

 Two cover-glasses of different sizes are fixed together by a minute 

 drop of Canada balsam, in such a way that at one edge the two glasses 

 lie exactly one on the other, while at the opposite edge one projects 

 slightly beyond the other. Ujion the edge of the smaller glass, which 

 forms a narrow step on the larger one, the spores were sown suspended 

 in water, and the whole arrangement placed in moist sand, from which 

 the water, containing a small quantity of a suitable nutrient substance, 

 rises between the two glasses by capillary attraction. Tlie light was 

 only allowed to reach the spores in a nearly horizontal direction in 

 some experiments, in a vertical direction from above in others, and 

 in a vertical direction from below in others. 



Without entering into details, it may be stated that the general 

 results obtained were as follows : — 



1. The rhizoids of all prothallia are negatively heliotropic, but 

 not positively geotropic. 



2. The germinating filament is orthotropic, positively heliotropic, 

 and negatively geotropic. 



3. The increase in breadth of the germinating filament is de- 

 pendent on the intensity of the light, but its direction is not deter- 

 mined by light. 



4. The surface of the cell is plagiotropic and dorsi ventral ; it 

 places itself at right angles to the direction of the light, and develops 

 an illuminated side, and a shaded side characterized by the presence 

 of rhizoids. 



5. In all prothallia of ferns the archcgonia are produced only on 

 the shaded side. 



This character of the appearance of archcgonia on the shaded side 

 only of the protliallium is characteristic of ferns alone among vascular 

 cryptogams; in Equisctaceie the case is ditlerent. 



Development of the Prothallium of Scolopendrium.l— As the 

 main result of a series of observatidus G. Beck states that when tlio 

 spore of Scolniicndrium germinates the cxospore is not ruptured, but 

 becomes softened in sucli a way that the germinating fihinicnt can 

 emerge at any spot. The protlialliuni lias in addition bristle-like 

 triclioraes. In no other essential point does tlio developnient of tho 

 prothallium of Scolopendrium differ from that of other I'olypodiaccae. 



• ' Bot. Zcit..' xxxvii. (1870) pp. r,07, 713. 

 t Sen tlii.-t .Jouriiiil, ii. (1S7!») pp. JAl, 917. 



t ' Vcrh. k.-k. y.ixA.-hot. (.Jc&oll. Wku,' 1879; sue 'Dot. ZLit.,' xxxvii. (1871)) 

 |). 091. 



