ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 311 



archegonial chamber and is stopped only by the hard seed-coat : the 

 suspensor when straightened out may be 5 cm. long. 



In the mature embryo the two cotyledons are free at apex and base, 

 but more or less completely fused in the middle region ; the long coty- 

 ledons constitute the greater part of the embryo. Zamiu therefore 

 differs from Ceratozamia which, according to Warming, has only one 

 cotyledon formed from part of the meristematic apex of the axis, the 

 rest forming the stem-tip. 



The authors suggest a series of gymnosperms from an embryonic 

 point of view. In the first series a gradual reduction in the number 

 ■of free nuclei is shown. In Ginkgo, Gijcas (?), and Zamia eight suc- 

 cessive simultaneous nuclear divisions precede wall-formation, resulting 

 in 256 free nuclei. In passing to Coniferales there is a sudden drop in 

 the number of free nuclei and a gradual further diminution. Taxus 

 has 82, Cephalotaxus, Podocarpus, and Taxodium 16, Thuja 8, and 

 Pinus 4, the higher numbers however not being entirely constant. 

 Further reduction occurs among the Gnetales, Ephedra sometimes show- 

 ing only a single free nuclear division resulting in two free nuclei, 

 while in Gnetum and Welwitschia no free nuclear division occurs at all. 

 These last-named forms have reached the condition of the embryogeny 

 •of angiosperms, in which the first division of the egg-nucleus is accom- 

 panied by wall-formation. 



A second series is based on the manner of wall-formation. At one 

 extremity stands Ginkgo with its numerous free nuclei equally dis- 

 tributed, and its wall-formation resulting in a proembryo which com- 

 pletely fills the egg. In Cycas there is a massing of nuclei towards the 

 base of the egg, and most of the remaining nuclei pass to the periphery 

 to form the parietal layer. In Zamia wall-formation appears only in 

 ■connection with the basal nuclei, and tissue-formation is restricted ti i 

 the basal region as in Coniferales. In the latter group there is ;i 

 gradual reduction in the number of nuclei, and a more definite setting 

 .apart of the function of each particular nucleus. Thus in Zamia the 

 snspensor cells are not recognisable until they begin to elongate : in 

 Taxus, Cephalotaxus, Podocarpus, and Taxodium there is no setting apart 

 of a distinct suspensor-forming layer; while in Thuja with its eight 

 nuclei, there is a distinct suspensor-forming layer, as also in the 

 4-nucleate forms. Thus the embryogeny of Ginkgo would be the most 

 primitive among gymnosperms, and that of Cycas more primitive than 

 that of Zamia which approaches more nearly the Conifers ; while such 

 forms as Taxus, Cephalotaxus, and Thuja show progressive stages from 

 Zamia towards Pinus. Ephedra shows the most primitive embryogeny 

 of the Gnetales, while Gnetum and Welwitschia most resemble the 

 ■angiosperms. 



Life-History of Ruppia.* — Sv. Murbeck records the following 

 results of his study of Ruppia rostellata. He suggests that pollination 

 may occur under water as well as on the surface, though definite proof 

 •was not obtained. During the development of the microspores the 



* K. Svensk. Vetensk. Akad. Handl., xxxvi. (1902) pp. 1-21 (3 pis.)- ^^e also 

 But. Gaz., xxxv. (1903) pp. 228-9. 



