628 SUMMARY OF CURRENT RESEARCHES RELATING TO 



concludes with some general considerations upon the trend of evolution 

 in the Zygopteridea3, namely, an ascending series as one passes upwards 

 in the geological succession ; and he epitomizes the matter with some 

 synoptical tables. 



Spermatogenesis in Equisetum.* — L. W. Sharp gives an account 

 of spermatogenesis in Equisetum. In an historical review he shows that 

 two general views have been put forward as to the morphological nature 

 of the blepharoplast in the Archegoniatete and Gymnosperms : (1) that 

 the blepharoplast represents a centrosome ; (2) that it is specialized 

 kinoplasmic or cytoplasmic material but not a centrosome. The follow- 

 ing is a summary of the results of his own investigations : 1. In the 

 early mitoses in the spermatogenous tissue of Equisetum there are no 

 centrosomes, centrospberes, or asters. 2. A minute granule, surrounded 

 by a weakly developed aster, appears in the cytoplasm near the nucleus 

 in each of the cells of the penultimate generation. This granule divides 

 into two, which become the blepharoplasts. 3. The two blepharoplasts, 

 each with its aster, diverge to opposite poles of the nucleus. First a 

 distinct central spindle develops, producing an amphiaster. 4. The 

 astral rays, which face the nucleus, form two cones of fibres which, upon 

 the disappearance of the nuclear memljrane, become the achromatic part 

 of the karyo kinetic figure. The blepharoplasts occupy the poles. 

 5. During the anaphases and telophases of karyokinesis the blepharoplast 

 enlarges, becomes vacuolate, and breaks up to a number of pieces, which 

 after further fragmentation unite to form the cilia-bearing thread. 

 G. In the metamorphosis of the spermatid the nucleus and blepharoplast 

 elongate spirally side by side, but have no connexion other than that 

 afforded by the undifferentiated cytoplasm. 7. The activities of the 

 blepharoplast in Equisetum, taken together with the behaviour of recog- 

 nized true centrosomes in plants and analogous phenomena in animals, 

 are believed to constitute conclusive evidence in favour of the theory 

 that the blepharoplasts of Bryophytes, Pteridophytes, and Gymnosperms 

 are derived ontogenetically or phylogenetically from centrosomes. 



Internodes of Calamites.t — P. Groom pubhshes a note on the 

 internodes of Calamites. These are characterized by a rhythmic recur- 

 rence of short internodes separated by a number of long ones. For an 

 explanation of this recurrence he compares the internodes in modern 

 Angiosperms ; and having called attention to certain features in the 

 rhythm of these plants, he enquires whether the Calamites stems con- 

 form in these respects with the woody stems of Dicotyledons. The 

 results of the application of three types of tests are given under the 

 following headings : (1) regularity of the period (cycle) of internodes 

 of Catamites stems ; (2) insertion of the branch-scars, and their dimen- 

 sions ; (3) nature of the leaf-scars on Catamites. The conclusion is 

 that each cycle in the characteristic rhythm in Catamites stems 

 corresponds to one season's growth in length. 



* Bot. Gaz., liv. (1912) pp. 89-119 (2 pis.). 



t Journ. Linu. Soc. (Bot.) xl. (1912) pp. 491-7 (figs.). 



