. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . 398 (Edogoniales precisely similar morphological characters. How have the androzoogonidia of thenannandrous species arisen 1 It is not at all probable that they have arisen from theantherozoids of the monoecious species by an increase in size of the antherozoid mother-cells, because two antherozoids almost invariably arise in each cell of the antheridium bythe division of the protoplast, whereas the entire protoplast of the androzoogonidangiu
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . 398 (Edogoniales precisely similar morphological characters. How have the androzoogonidia of thenannandrous species arisen 1 It is not at all probable that they have arisen from theantherozoids of the monoecious species by an increase in size of the antherozoid mother-cells, because two antherozoids almost invariably arise in each cell of the antheridium bythe division of the protoplast, whereas the entire protoplast of the androzoogonidangiumforms a single androzoogonidium. Seeing that this is also the case in the formation ofboth the androzoogonidia and gynozoogonidia of the rnacrandrous species and in thegynozoogonidia of the nannandrous species, it is reasonable to suppose that the smallandrozoogonidium of the latter has arisen merely by a reduction in size, which has goneon hand in hand with a greater sexual differentiation. The specialization has become suchthat the audrozoogonidia are attracted to the vicinity of the oogonia and only germinate. Fig. 253. (Edocladium protoncma Stahl. A, vegetative plant showing the colourless rhizoidsand two of the resting cysts, x 41. B, development of a male branch, x 330. C, a branchwith an oogoniiun, x 230. D, longitudinal median section through the zygote, x 230.(After Stahl, from Wille.) either on their walls or on the walls of the supporting cells. The male plant which is thendeveloped is so reduced that there is at most only one vegetative cell, or sometimes none,and one antheridium consisting of from one to five cells. The reduction of the malefilaments to nannandria is to be correlated with the fact that the antherozoids are setfree in the immediate vicinity of the oogonia, and, therefore, fewer of them are required inorder to ensure fertilization. Moreover, vegetative cells are unnecessary except as asupport for the single antheridium, for which one cell easi
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