162 



NOTES ON DIPTEEOCAEPS. 



Figure 2. The emb^o x 3 (from 

 the basal end of the fruit :) pi. pla- 

 centa ; cot. i. inner cotyledon : cot. o. 

 outer cotyledon. 



Figs. 3 and 4. Fig. 3 (above) the 

 embryo is section near the rounded 

 end of the seed: Fig. 4, (below) the 

 same toward the pointed end. 



The outer cotyledon (cot. o.) when seen from this point of 

 view, appears to be very much less bulky than the inner and is 

 indeed a little less bulky. Each is two-lobed (see fig. 8), these 

 lobes being packed in the seed in the upper half of the loculus, 

 where they surround the radicle. 



On cutting the embryo transversely near to the end which is 

 represented in figure 2, the two cotyledons are seen doubled round 

 the placenta as in figure 3. But when we take a transverse section 

 towards the other end, we get their lobes in section surrounding 

 the radicle and hypocotyl as in figure 4, the two lobes of the inner 

 cotyledon embracing the placenta. 



At maturity when the shuttle-cock-like seed falls, spinning 

 into the sparse herbage and leaves on the floor of the forest, the 

 embryo plant is full of chlorophyll and in such a state that it must 

 germinate without delay or die. By reason of the way in which it 

 falls, there is a considerable probability that it comes to rest with 

 the radicle directed upper-most, and a certainty that it will not be 

 directed downwards. The seed germinates ; the cotyledons by 

 growth and in straightening themselves rupture the thin ovary 

 wall and seed coats, not along two constant lines but along two lines 

 from top to base on opposite sides, generally rather more than 180° 

 removed from each other on the side of the partial septum, so 

 that this portion of the husk is rather larger than the other: then 

 the hypocotyl elongates and curves to direct the radicle into the 

 soil (fig. 5) ; if the radicle succeeds in anchoring, a tendency in 

 the hypocotyl to straighten itself which now succeeds to the other, 

 pulls the cotyledons from the loosely imprisoning fruit-walls, and 

 the stage which is seen in figure 6 passes over to that seen in 



Jour. Straits Branch 



