ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 17 



• > 



than in the vertical roots. The xylem of the absorptive roots is com- 

 posed mainly of ducts, that of the vertical roots consists almost entirely 

 of wood-cells. 



#. Physiology. 

 (1) Reproduction and Embryology. 



Female Prothallium of the Stigmatee.* — In his researches on the 

 comparative anatomy of flowering plants, Prof. Ph. van Tieghem proposes 

 the following new terms : — Vascular plants he now terms Wiizophytes, 

 divided into Exoprotltallese (Vascular Cryptogams) and Endoprothallese 

 (Phanerogams), according as the prothallium (unisexual or hermaphro- 

 dite) is free in the surrounding medium, or (always unisexual) enclosed 

 within the adult plants. The latter he has already j again classified 

 under Astigrnatre or Nudiovulatae (Gymnosperms) and Stigmatae or 

 Tectiovulatae (Angiosperms). 



In the latter group he proposes to apply the term mesocyst to the 

 (definitive) central nucleus of the embryo-sac with which the second 

 antherozoid fuses, and the result of this fusion is the trophime. The 

 ovum (fertilised oosphere) and the trophime are, in the Stigmatae, the 

 sole survival of the female prothallium. For the result of the develop- 

 ment of the trophime he restores the term albumen, the sole function of 

 which is, at one time or another, to serve for the nutriment of the 

 embryo. Nothing of this kind occurs in the Astigmatae, where there is 

 a true endosperm, not the result of a sexual fusion, but the remains of 

 the female prothallium, serving the same purpose as the albumen of the 

 Stigmatae. There is in the Astigmatae neither mesocyst, trophime, nor 

 albumen. 



While the oosphere perishes without further development if it does 

 not receive an antherozoid, the mesocyst is able to develope even if it 

 does not receive the antherozoid which converts it into a trophime. 

 There are examples of adventitious embryos, not the result of a sexual 

 fusion, as in Coelebogyne and in certain Balanophoraceae ; and, on the 

 other hand, there are plants in which the mesocyst does not develope 

 into an albumen, as in the Orchideae, Canneae, Alisrnaceaa, and Vicieae. 



Double Fertilisation in Compositse.f — According to W. J. G. Land, 

 the following is the process of inrpregnation in Erigeron philadelphicus 

 and Silphium laciniatum. 



In Erigeron the pollen-tube passes down a short distance into the 

 embryo-sac, and discharges the male cells, which bore their way through 

 the surrounding cytoplasm. One male cell fuses with the oosphere 

 nucleus, the other with the endosperm nucleus. This latter, after 

 fusion with the male cell, rapidly divides, and soon fills the sac with 

 a mass of nuclei. The fertilised oosphere remains some time in the 

 resting condition, doing little beyond developing a dense membrane and 

 becoming slightly larger. The first wall is transverse. 



In Silphium the polar nuclei fuse long before fertilisation. The 

 pollen-tube passes down into the embryo-sac and discharges two male 



* Journ. de Bot. (Morot), xiv. Q900) pp. 100-4. 



t Cf. this Journal, 1897, p. 313. 



j Bot. Gazette, xxx. (1900) pp. 252-60 (2 pis.). Cf. this Journal, 1900, p. 483. 



