Howe: Phvcological studies 507 



starch appears to increase at the expense of the chlorophyl. Some 

 of the spores sliovv a pronounced polarity, or perhaps it may be 

 called a beginning of germination, while still in the sporangium. 

 Thus, in the second spore from the right in figure 2i, the foot or 

 base of the young plant is plainly manifest. Such basal parts have 

 less chlorophyl and starch than the remainder of the spore. The 

 membrane enclosing the spore is usually thin and delicate and often 

 scarcely demonstrable. When the spores are well formed, there 

 is a peculiar aggregation of granules at the apex of the sporangium 

 (figures 21, 24) and this appears to be followed soon by the 

 rupturing of the sporangium wall in this region, forming a rather 

 wide irregular opening. All the spores in any single sporangium 

 seem to be discharged at about the same time, for the sporangia as 

 found, with a few possible exceptions, are either empty or contain 

 their full complement of spores. Very little is known of the 

 history of the spores on leaving the sporangium. Figure 19 

 shows a spore which had been caught at the mouth of the spor- 

 angium and had evidently begun its extra-sporangial growth, form- 

 ing an evident foot and the first "bead" of a moniliform filament; 

 this was firm-walled and very brown. 



The large size of the spores (130-300// x 66-120//), their 

 heavy load of starch, and their occasional development of an evi- 

 dent foot while still in the sporangium, make it practically certain, 

 in our opinion, that these bodies are not self-motile, /. e., that they 

 are aplanospores. Yet, the thinness of the surrounding membrane 

 and the fact that none of the bodies has thus far been found ger- 

 minating on the surface of the thallus (if we except the captured 

 one shown in figure 19) have suggested the possibility of their 

 being synzoospores. However, it is much more probable that we 

 have to do with aplanospores, perhaps analogous to those which 

 occur in smaller size and larger number in Gomontia polyrhiza 

 (Lagerh.) Born. & Flah. or to those which have been described as 

 occurring singly in Vaucheria haniata and V. gemmata.^ 



E. On the American species of Avrainvillea 

 Tn a former paper t we alluded to some of the difficulties in the 

 way of distinguishing species in the genus Avrainvillea and com- 



* Waltz, J. Jahrb. Wiss. Bot. 5 : 132, 133. 1866. 

 t Bull. Torrey Club 32 : 565-568, 586. 1905. 



