54 THE MICROSCOPE. [April, 



10 microns or 1-2500 of an inch in diameter. Each one of these 

 is a single cell. The lower part, somewhat longer than the pro- 

 jecting part, clasps the body of the limb, reaching down to the 

 axil of the next cell. 



These surround the vascular centre of the branch. They really 

 seem by their union to form it. making a most excellent arrange- 

 ment for receiving the pollen grains. In English blue-grass these 

 are about 20 to 30 microns, or averaging about 1-1000 inch in 

 diameter; in orchard grass and K. blue-grass, about 30 to 35 

 microns. These grasses are good for studying the sprouting of 

 the pollen grains and for tracing the tubes down the style to the 

 ovule. Those grasses that have pale white stigmas are much to 

 be preferred to those having red or purple stigmas. 



Kentucky blue-grass blooms in May and June ; orchard grass 

 soon follows ; next comes the English blue-grass, in June and 

 July. It has a very delicate plumose, clear stigma, and makes a 

 good study. 



In the common oats I have found a stigma that offered much 

 interest. The pollen grains are larger, 40 to 50 microns, or 

 1-625 to 1-500 of an inch in diameter. The " red top " is a very 

 good grass for study. The late flowering grasses, as the Muh- 

 lenberg grasses, Panic grasses, etc., with red stigma, do not af- 

 ford so good material. The common timothy is of all the very 

 best. At the right time it gives the grandest sight among the 

 pollen tubes that I have seen. Although timothy blooms in July, 

 a few heads can be found until the hard frosts kill the heads. 



In 1S91 I mounted some pollened timothy stigmas in glycerin, 

 though they look the best in fresh water. . Dr. Stokes, to whom 

 I sent a slide, wrote : 



" Your slide of pollen tubes is most remarkable. Never have 

 I observed pollen tubes as they are in the mount you kindly sent 

 me. I have seen the tubes, of course, but never such an exhibi- 

 tion of them." 



On a clear summer morning, with plenty of dew on the grass 

 and no wind, if the timothy is in blossom, its pollen sacs will 

 be seen hanging on the filaments at daylight, and the plumose 

 spreading stigma, moist in the morning dew, projecting out be- 

 tween the palets ready to receive the pollens. As the sun shines 

 on the pollen sacs they burst open. If now we give the stalk a 

 gentle shake, we shall see the numerous pollen grains, dust-like, 

 falling and floating off in the air. If the morning is windy, much 

 of this will be blown away. We will not get a stigma well-filled 

 with sprouting pollen grains. But when the morning is still, many 

 more of the grains will lodge on the plume of each stigma, and 

 because of its closed head, much more in timothy than in the 

 other grasses. Do not disturb the head until near noon. Give the 

 pollen grains time to sprout and the tubes time to descend the 



