INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 917 



sjiore Oldens at tlie poiut of junction of the three ridges in radiate, or 

 in tlie middle of the single ridgo in bilateral spores. Through this 

 opening protrudes a papilla, which develops protoplasm and chloro- 

 phyll like a young cell, and, either at once or after a short time, puts 

 out a second papilla, the first rhizoid ; both cells subsequently de- 

 veloping in various ways. The usual explanation of these appear- 

 ances is that when the exosjiore bursts, the endospore develops and 

 forms the wall of the first cell of the prothallium, as also usually of 

 tlie first rhizoid ; the contents of the spore passing over into these 

 two cells. 



In following out this process, Rauwenhoif met with the difficulty 

 that, although chemical tests failed to detect the presence of cellulose 

 in either the endospore or exospore before germination, this substance 

 is clearly present in the papilla and in the parietal portion of its 

 contents in the earliest stages of germination. He gives a detailed 

 description of the phenomena observed in the germination of the 

 spores of Gleichenia, which are especially favourable for observation, 

 owing to the transi)arency of the cell-wall of the spore, and comes to 

 the conclusion that the source of the wall of the first prothallium- 

 cell and of the first rhizoid is not the endospore or inner shell of the 

 original wall of the spore, but a new cellulose wall secreted out of 

 the i^rotoplasm of the spore before it opens, and increasing in the 

 ordinary way by intussusception. 



The source of the ordinary interpretation of the first stage in 

 germination is doubtless a false analogy with the process of develop- 

 ment of the pollen-tube, which undoubtedly results from the growth 

 of the intine or inner coating of the wall of the pollen-grain. 



That the germination of the spores of other vascular cryptogams 

 will be found to agree with that of Gleichenia rather than with the 

 development of the pollen-tube of phanerogams, where observation 

 of these processes is possible, is concluded by IJauwenhoft" from the 

 following considerations. A section of pollen-grains in which the 

 pollen-tube has begun to develop, shows that where the tube has 

 broken through, the wall consists of fewer layers than elsewhere, 

 that is, of the extine only. In fern-spores, on the contrary, the wall 

 is of the same thickness, and consists of as many layers after germi- 

 nation as before ; showing that the protruding wall of the papilla 

 must be a new membrane. The changes in the contents of the spore 

 on germination are also much more extensive than those of the 

 papilla of the pollen-grain when the tube is formed. The intine of 

 pollen-grains consists, moreover, of cellulose, which is certainly not 

 generally the case with the endospore of such fern-spores as have 

 been carelully examined. This explanation also corresponds with 

 what is known to take place in the formation of the zygospore of 

 Spirogyra and other Conjugate, as well as with the processes observed 

 in the germination of the spores of Equisetacete, Hepaticae, and 

 Bryine?e. 



Bilateralness of Prothallia.* — In opposition to the opinion of 

 Bauke,| Leitgeb still maintains his view that the bilateralness of the 

 * ' Flora,' Ixii. (1879) p. 317. t See tins Journal, ante, p. 4r)l. 



