io8 



LECTURE VII. 



and nuclein but without a cell-wall— the oosphere, taking up into itself very small 

 movable corpuscles, the spermatozoids, and being thereby impelled, by the secretion 

 of a cell-wall, to constitute itself into a true cell surrounded with a membrane, from 

 which a new plant now proceeds. This is the case in all Mosses, many Algae, and 

 all Vascular Cryptogams. In the Phanerogams, however, the oosphere is incited to 

 further development by a substance passing over into it from the fertilising pollen- 

 tube. According to Strasburger's statement it appears that this fertilising substance 

 is essentially the nuclein of the pollen tube. Zacharias and Schmitz are-of opinion 

 that in the Cryptogams the fertilising spermatozoid originates from the nucleus of 

 its mother-cell ; so that fertihsation appears to be essentially a matter of the trans- 

 ference of the substance of the cell-nucleus, especially of the nuclein, out of the 



Fig. la^.— Vaiccheria sessilis (X 30). A exil of a swarm-spore (sp) ; B, C its germination ; 

 D jferininating plant devoid of a root i H, F older plants with roots {w) ; sf the original spore 

 still visible as a swelling ; os and A (in F) sexual organs. 



male organ into the oosphere ^ A further pursuit of this topic, however, belongs 

 to the theory of sexual reproduction, to be treated of later. 



Finally, with reference to the facts presented hitherto, we have still to cast a 

 glance at the non-cellular plants, the- Cceloblasta. These plants are often of 

 considerable size, and develope roots and shoots, even leaf-forming shoots, fructi- ■ 

 fication, and sexual organs, without their internal substance being converted by cell- 

 division into a system of chambers. A plant of this nature, as we have already learnt 

 from several examples {Caulerpa, Bryopsis, Vaucheria, Mucor), is a much branched 

 vesicle, the various protuberances of which represent the different organs; roots, 

 shoots, leaves, sexual organs, sporangia, and so forth. The wall of the vesicle is 

 a cell-membrane, and its contents protoplasm and cell-sap ; and, with reference solely 



' On the nature of the spermatozoa, see Zacharias, Bpt. Zeitg. 1881, Nos, 50, 51. 



